From what I've understood, the girl is the daughter of your wife, she's 10 years old, speaks a different language and has only recently moved in with you and your wife.
Within such a situation, where the relationship is brand new, I would suggest focusing on first and foremost establishing a relationship with the girl where you can both get to know each other and start learning how to communicate effectively and build trust. As such, I suggest speaking to your wife about her handling the 'raising/education' aspect of caring for the child while you focus more on enjoying yourself with the child, taking walks, playing together and similar activities.
Because here it is important to place yourself in the shoes of the child. Imagine coming to a different country, not knowing the language and having to live with a man that is now your mother's husband. This can be quite a daunting experience for a child and many of her reactions may be originating from this experience. Therefore I would not focus on discipline or education at all in the beginning, especially if what you are doing is coming from a starting-point of reaction and not as a directed decision based on an understanding on how to raise/educate a child.
I surely understand that it is a difficult situation for all three of you -- and this is why I suggest making an agreement with your wife that she will be the primary responsibility in educating the child in the beginning, so that you can focus more on simply getting to know her and establish effective communication. This will also alleviate some of the pressure of you.
The primary point I suggest taking on within how you approach the child, is to in all moments place yourself in her shoes - meaning consider the situation from her perspective and accordingly look at what would be the most supportive course of action to take.
I can share with you that I actually had a similar experience, where when I was 10 years old, my mother moved us in with her new boyfriend and although it wasn't in a new country where I couldn't speak the language, this was a very difficult experience for me. Also within this consider that a 10 year old already has an entire life behind her and as such one cannot simply re-start educating them or raising them, but have to also work with who they are now and see them as a being.
I am glad that you are asking for support and sharing yourself here because this is surely a difficult situation that many parents and stepparents face and it can be quite tabooed, especially for stepparents for whom it can be difficult when suddenly having to live with a child. It is much different raising a child that you've known since they were born. So this point, as you continue to walk it and expand yourself - educating yourself to become a parent - can be of great assistance and support for others facing similar situations.