Can someone please tell me how I can fix this?

It said that everything was fine when I started Voobly, however, when a game starts, I can't join because it says that the language files aren't found.

Can someone please?

Are you using the CD version or the HD version+compatibility patch?

If compatibility patch: https://support.voobly.com/display/vkb/KB1054+Clean+installation+of+Aoe2HD+with+compatibility+patch

If CD version: Is the text there if you start a game offline? (Go into the installation folder -> age2_x1 -> start age2_x1.exe)
If not, either reinstall or download the appropriate language files from here: [You must login to view link]

@jineapple

Thanks a lot! It works perfectly now!

Now just 1 other question:

My game looks like it's straight from the 1999 version. It just looks completely different. What is wrong with it?

My Steam version looks fine but the Voobly version looks just very bad.

How can I fix that?

Define "very bad"? Do you have screenshots maybe? The two versions will look a bit different (for example, fog of war is done differently, the water is different if you use animated water, etc.) but nothing that should make you say it's "very bad".

I don't have a garrison button, the screen is like 720/720, hotkeys don't work, everything is zoomed to like 1,5x original format, it all looks pixelated as hell and it's a bit darker.