I don't know if this work the same way in extrabiomes, but when i localized the tooltips for mDiyo i did this:

import net.minecraft.util.StatCollector;

StatCollector.translateToLocal("extrabiomes.tooltips")

And then in the en_US:

extrabiomes.tooltips="the tooltip"

I'll be looking into adding localization support for tooltips in our next release.

Tooltips are now able to be localized so I am closing this.

Thanks for the recommendation I'll make sure to give it a look. The tool tips were one of the last things that we added so I didn't get to doing a ton of research on the topic of localizaion.

The one issues that I see is that how I wrote the tooltips since I wasn't worrying about localization, will need a bit of a rewrite, as they stand the tooltips can have variable number of lines an all I have to do is add another string to the reference. I haven't looked at StatCollector to see if it has a method to see if a key exists, or how it responds to a missing key, but I may be able to make it work either way.