Filter by TLD to mimic a language filter.
Allow URL/Domain filters with only two characters, eg .no or .se. Or by using wildcards, eg: *.se
You already have a filter for domains, ie "buzzsumo.com" but an easy implementation to sort of filter on language is to allow juse the TLD.
Eg: Most swedish sites reside either under the TLD .se or under a gTLD like .com. And if they are under a gTLD quite often the URLs path start with the language code: thesite.com/se/...
So a search for: "*.se OR */se/*" would probably hit most of the swedish and filter out others.