Today I observed a user who was trying to load an article that was in progress of translation. It failed, and the article's content couldn't be seen. JS console showed an error:
Uncaught Error: Syntax error, unrecognized expression: #.D7.9E.D7.A7 ... etc.
This happened in translation of "פתח תקווה" from Hebrew to Spanish.
This comes from ext.cx.translation.loader.js line 311.
jQuery probably tries to parse #.D7.9E.D7.A7 as a selector, and it's a non-ASCII string from article content that was encoded in a way that jQuery cannot parse.
This causes apparent data loss—the data is probably stored in corpora, but cannot actually be loaded. Non-ASCII strings are very common in Wikipedia, so it's an important issue to fix.
There were many similar complaints on Talk:CX lately about such problems, and this is probably the reason.