Using the questions is also a great option, one or two is sufficient with the above addons. Making the questions related to your content is also advised.
Last post by ahrasis -
Like any other addon, use package installer and follow instructions there after install. Language can be set per forum board, also in multi tenancy addon per each tenant forum.
I was looking for a convenient post to "jump in on" and ask a basic question, but you've got queries all over the board with various add-ons and plug-ins, so I'll pick this one..
What was the last known "bug free" forum and server configuration you had (if you know) and can you "roll back" to that configuration?
At this point, I would not be surprised if it's necessary to wipe everything, do a fresh install, test the heck out of it with actual users (who will do things in ways you would never think of to try), and then back that up when you know it's stable, and then slowly add a mod or add-on one at a time and make sure that works before adding something else. That way if/when something breaks, you have a known-good baseline to go back to. As it stands now, we have no idea what mods, add-ons, patches, you have installed, what you have installed and removed (most of?), never mind what your server configuration, database, etc. is. It's quite possible what you have now is the first iteration of that combination of software anywhere on the planet..
And a known good baseline is especially important if you download and install a mod or add-on that was last tested with, say, EH 1.0.9 running php 5.2 more than 12 years ago, and has few support comments and none in the last 9 years. Heck, there may be some out there someone tried to port to EH that never worked right. Consequently, there is no way to know if the error you encounter is related to the forum software, the server configuration, or the last 7 mods you installed, 4 of which you tried to uninstall because it didn't work, or you didn't like...
Again, do you have a known-good forum configuration you can restore to?