Currently, one individual campaign can only be in one language (because the 6 ads in a Promote campaign should be the same ad, but resized). So you cannot have eg the Finnish, English, German versions (6x3) in one campaign.

Apparently in other platforms it is possible to have multiple language versions within one campaign.

If you want to have multiple language versions in Promote there is A) no language based targeting and B) you'd need multiple campaigns and therefore a lot more campaign spend.