Great. They can go through the chaotic city - a purple preteen attempts to pickpocket Tanya -

Tanya isn't going to be surprised by someone sneaking up on her! (For humanly possible levels of sneaking up, not Golarion-bullshit levels.) She constantly scans her surroundings and uses optical warping to maintain little rear- and side-view mirrors floating next to her head. If a random kid could touch one of her men unawares she'd tell them they deserved to lose their wallet for the abysmal failure of situation awareness. (Also, the hand wouldn't make it through her barrier.)

She's on edge but she doesn't point her rifle at the kid, only flies higher up and fixes him with an unimpressed stare.

He abandons the attempt and disappears into the crowd. Belmarniss stops to watch if Tanya's going to do anything else about this, and then when she doesn't sighs in relief and continues.

Tanya grew up in an orphanage; she understands this kind of thing happens in developing societies that aren't rich and civilized enough yet, similar to street begging. Normally a pickpocket would have the sense not to go after an aerial mage in uniform, but normally the mage is able to arrest them. Anyway, she has much bigger worries on her mind right now.

They have a longish walk through the city. No one else tries to start anything, though a couple times Belmarniss has to engage in brief chat with random purple people (the tiny and tusky people never attempt to address her).

Tanya can come up with many theories for what's going on. Multiple races (*) with different cultures or languages or typical occupations or even social castes? An aerial mage (of a species not attested locally) not eliciting stares or requiring explanation beyond a few sentences? Belmarniss (alone in a small city?) knowing Germanian, but only a little? An underground settlement that doesn't know (or forbids) contact with the surface even though they must trade with it for food? 

But she restrains herself from guessing. Besides not having any hard facts, this is all fruit of the poisonous tree: if Being X sent her here then everything she sees might have been selected for her to elicit a harmful initial reaction. She will wait to see what Belmarniss is leading her to, because it might be that she's leading her to someone who actually knows Germanian, and then Tanya will be able to reason rationally from facts instead of guessing. 

(*) In the Earth sense, obviously.

Belmarniss takes her into what might, in cave people terms, be a sort of suburb. Tunnels and ladders and hallways and stairs and more castings of that one spell she likes for rough terrain, lower traffic, more curtained-off or even door-having apertures blocking casual entry as they pass through.

Finally they are in a relatively large space with little alcovey areas around the edges. Belmarniss talks to some people - purple teenagers younger than herself, looks like - and gets directions that send her to a specific alcovey area. The purple teenagers gawk at Tanya but do not attempt to pick her pocket.

Tanya still has no idea what the earth-probing (?) spell does! Presumably Belmarniss already knows everything she wants to about materials right here in the city? ...and in the caves too, if she lives here then she presumably wasn't exploring before but changed purposes on meeting Tanya (for which she is grateful, if everyone else can't or won't talk to her).

Gawking is fine. (She wonders if they're mages and can see her spells like she assumes Belmarniss can.)

She's nervous about being in an even semi-enclosed space; this isn't a cave but there are many more people around here. She's been on high alert since they entered the city; now she will keep an eye on the sky open side of the alcove.

The alcove is furnished like an office, if you ignore that the desk and the chair are made of bones. (The bookshelf, at least, is carved right into the wall.) It's got a closed stone trapdoor in the floor that isn't particularly trying to be hidden but is locked. There's a purple woman there who greets Belmarniss in a friendly sort of way; they have a talk.

The furniture is made of bones? That is sure an aesthetic choice that Tanya might react negatively to if she hadn't just decided not to react to things until she can properly talk to people!!!

(Some units have skull insignia. Some churches have ossuaries that people can visit. Tanya is going to ignore this very strongly, because it does not matter.)

The conversation concludes with the woman whose office they appear to be visiting pulling a book out of her desk and paging through it. Belmarniss leans on the wall with a patient-waiting attitude.

Tanya is willing to wait a little. (She really hopes Belmarniss isn't going about her own business while letting Tanya tag along and wasting her time.)

They'll be waiting about fifteen minutes.

This had better be worth it. But what else is she going to do, accost random people asking if they can understand her? 

(Maybe she's looking up something that would help, like the telephone or address of someone who speaks Germanian.)

...she consults the map Belmarniss drew for her earlier, trying to trace the path they took to get here and to match the city's schematic with what she's seen of it. (She hasn't seen much, because she didn't want to light it all up.)

The map is not very detailed but it does not contradict anything she saw outright if she makes some reasonable assumptions about the map's liberties with scale and granularity. That would put them about... thereish? She could wave the map at Belmarniss in case that gets her to point at things.

Tanya can't think of anything she particularly needs pointed out, and can't communicate well anyway. 

She can do 'hurry up and wait'; she hasn't decided how long she should be willing to wait for, but she'll wait for fifteen minutes.

Eventually the woman finishes with her book, puts it back in her desk, gets up, and holds out her hand to Tanya. "Tongues?" she says.

"I'm sorry, I don't understand." But she'll shake the offered hand.

The woman holds firmly onto the offered hand for three and a half seconds while she casts: "Tongues."

"Did that take okay?" Belmarniss asks. "What're your most urgent confusions?"

Tanya can, of course, sense the woman casting. Her instincts are screaming at her not to let a stranger cast a completely unknown spell at point blank range, even if she has no visible weapon and the amount of mana she's using isn't enough to penetrate Tanya's shield and barrier. Magical technology is evolving quickly and the mana-to-heat conversion efficiency of current orbs is definitely not any kind of limitation of physics.

She could be about to kill Tanya on the spot! Never mind that she has no shields or other active spells to protect herself or Belmarniss from the backblast of the explosion. Never mind that Tanya is yet to see anyone here achieve a magical effect stronger than a weak light. What if her spell has an effect Tanya's shield isn't meant to protect from that knocks Tanya out? What if Belmarniss led her here so they could steal her orb? Why take a risk, any risk?

Tanya has been thinking, since she saw the city. Suppose she has been sent a completely different world, where she knows nothing and no-one. All her hard-won skills and knowledge, her preconceptions and reactions, could be wrong here; in fact this world might have been adversarially chosen to produce that effect. She doesn't even have the luxury of growing up as a baby and slowly learning about the world. What is the rational thing to do, if she isn't sure of the outcome of any possible action? How can she tell what serves herself and not being X in a situation he might have set up?

When you meet complete strangers, game theory says that you should try to cooperate at least once. If Tanya has to choose between the failure modes of "Tanya attacks complete strangers, turns new world against herself" and "Tanya foolishly trusts complete strangers, letting them attack her" then she'd rather be the second kind of person. There's more to her than the professional soldier on a hair-trigger reflex. 

Tanya doesn't know anything about Belmarniss and her intentions. If Belmarniss isn't rational, or if the local culture endorses robbing strangers, she might attack Tanya. But in those cases Tanya would lose anyway; she can't stand alone against all of local society. (Except in the sense that she could probably kill all of them, but what would be the point?) And if the local equilibria don't favor cooperation, then maybe Tanya doesn't want to live here. Maybe she'd rather die and tell Being X to his face that she is tired of his bullshit than live in a world where she has to assume the worst of people to survive. 

She speeds up her reactions and powers her shield as much as she can. Takes her service pistol in her free hand. And lets the woman holding her hand complete her spell.

...so Belmarniss was only pretending not to speak Germanian before? She doesn't even have an accent now! "What did you just do and why wouldn't you talk to me before?"

Tanya hopes there's a good explanation for all this! On the upside, that spell wasn't an attack after all.

"...I just asked Instructor Johysis to cast Tongues on you, because I do not speak your language, never have, and am unlikely to ever learn it. You will notice if you pay close attention that I am not speaking it now. Before, I was using the spell Comprehend Languages and repeating a few words you had already said to me. Because I do not speak and have never spoken your language. Tongues will last maybe an hour and I do not have infinite favors to trade for more castings, so please try to be a bit quicker on the uptake."

That makes no sense and Tanya is about to tell her so when her brain catches up with her ears because that was not Germanian or any other language that she knows, except that apparently she does know it? What the fuck, brain?

"...I suspect I still don't understand. I - already thought I probably came here from a different world. Our magic doesn't do... translation?"

That's not even right! Magic could in theory do translation, because translation is at least possible as an, an algorithm - Tanya's first world had very crude computer translation (but only between two languages the algorithm knows, obviously you can't translate a completely alien language from scratch)... But whatever this is, it doesn't feel like translation? It feels like just knowing how to speak in a language? The word for 'word' sounds like this and Tanya can tell this without even speaking out loud but she never learned this fact???

In some sense this isn't more surprising than going from a world without magic to one where some people have an extra mental lever that does stuff outside their bodies. Scientists can detect and measure magic (although only by relying on other mages operating the detectors) so it's no more mysterious than magnetism (i.e. very mysterious but undeniably real)... Tanya can't quite put her finger on why she feels this 'Tongues' spell cuts against her world's paradigm. Maybe a magic researcher from back home would look at it in glee. Maybe this vague feeling of dread that she has absolutely no idea what is and isn't possible anymore is because she's used to weighing everything as a potential threat and she should remind herself to think more of the benefits of technological development.

"I don't know what you can do," she concludes somewhat hesitantly. "Earlier I asked you about the surface because where I'm from people don't live in caves. ...Assuming this is an underground cave."

"Humans don't live in caves; we do. The reason I can't take you to the surface is because there's a bunch of monsters around and I don't know the way. But I do speak the language most popular upstairs and then a few more besides and you don't, so I'm not sure how much it'd help you to brainstorm ways you could get up. - let's get out of Instructor Johysis's office, shall we."

Humans don't...? Monsters? The translation isn't perfect.

(Tanya does not seriously reconsider that a bunch of non-humans might live in a cave with secret advanced magic on her planet.)

"...I will follow you."