When I launch XnView for the first time it is in English. I go to Tools->Options->Interface->Change language into Russian, it says you must restart XnView, but the language is changed immediately, without restart. However after restart it changes back to English. I've found that if I launch XnViewPortable.exe, change language and then restart - language stays in Russian(same thing when it starts after double click on some image). But when I launch it through portableapps.com platform it switches back to English. Please check this out.
XnView will use the platform's language, so if you have the platform set to English, that's what will be used, instead of Russian.
[EDIT] I just tested, and am able to confirm it works as above, correctly.
Whoa! It really is so. Helpful feature, but unknowingly it becomes weird))