I’m native speaker of Ukrainian and Russian. Most of my 10 years of experience I have tested projects with interface and documentation in English. A few projects I worked on had Russian interface and documentation.
One international software company I worked for supported in their software a lot of interface languages besides English: Spanish, Italian, French, German, Russian, Finnish, Chinese Simplified, Chinese Traditional are those I remember and worked a bit with. Dealing with interfaces in European languages is not that hard after you know some English (you can guess or Google-translate what you see), but Chinese hieroglyphs is not something I could understand to any good degree so far and even type what I see. Had to switch interface language or to put next to the Chines interface the client with the same interface in English.
Had also to work a bit with interfaces in Hebrew and Arabic on other project, but the story was the same as with Chinese: I could not read any word, and looked at the interfaces only to check that they are there.