The language of the email invite is sent in the language of your dashboard at the time of sending. this means you can just switch the language of your dashboard by groups of languages you are planning to send to.
Regarding the invite itself, the language is set under the “Wedding Details” edit page. You can only have one language per invite.
For your needs you have two options:
1. Setting the language to one language, and inviting all the current language speakers. Then after they all RSVPed, you can switch to the other language and invite all the rest of your guests. This is ultimately less ideal because guests will return to your invite for directions and to upload photos.
2. Open a separate invitation for every language and when the time comes, just export your song list and guest list from both, and combine them in excel. This is the better solution.