Is it okay to have a multi-language deck?
Yes.

Under official Magic, they're all the same card regardless of the printed language. From the comprehensive rules:


  201.2. A card’s name is always considered to be the English version of its name, regardless of printed language.


From the tournament rules:


  It is not required that players play with cards that are printed in the native language of the area in which the tournament is being run. If a player needs to know what a card does, either because it is in a language they cannot read, or it is a textless printing, they may call for a judge and ask for the Oracle text.