Erm... I did not try to translate with xml. First there is a pot-file and second one can translate every single phrase. Both work.

I Have the wpforo-es_MX.mo and wpforo-es_MX.po but i don't know how i put

Please read this support topic:

https://wpforo.com/community/faq/how-to-translate/

IMPORTANT: After all kind of translations you should click on [Delete Phrase Cache] button located in Dashboard > Forums > Dashboard admin page:

i delete cache and user cache don't work and . Use .POT file, it's located in /wpforo/wpf-languages/ directory.

how use?

I Go to wpforo.pot and translate:

Later: Save and upload

and: 

don't work and  and  ?1

Finally: 

Why!?

Phrases:

All Phrases Spanish..