Shouldn't be too difficult. The main thing you'd need is a dictionary that's as close as possible to covering the entire language (ie a digital-first one rather than a digital representation of a paper dictionary), and at least one but ideally several frequency lists. Ideally in the JSON format that Yomichan uses, as that's what the script for generating the data currently expects, but if not then the data can always be massaged. Then you just need to replace the specifics in the app (hardcoded frequency list names etc) with the stuff for your language.