Just wanted to let you know that I really like what you have here Rimelek, very good job.
And I'm sitting here thinking that you could not do $hu['missing_index'] return a fallback/default string in another language if the index doesn't exist.

Now a few questions, since I haven't yet tested the code:

• what if an index is missing altogether? Can it return "Missing index"(a predefined string) or "missing_index"(the actual missing index as a string)?
• does is support plurals? I haven't seen any example, just curious.

Keep it up! 👍