Go get something out of Project Gutenberg that is popular, and not too long.
Translate it into 3-4 major languages. Give those away for free.
Even better, test your translations against actual public domain translations if they exist, and be transparent about WER for each language.
If you want this to be a business, you’re going to have to do some serious business-like things.
Translation models are getting better all the time - it's a weird artefact of transformer architectures that got missed in the GenAI hype, that they're pretty great at translation, especially across languages with smaller training corpuses - but you should definitely know if the text you're reading is only likely to be 90% "correctly" translated.
Especially this. I often come across AI products that claim to do well in 100+ languages, show some really good DE/FR/SP/RU examples, then I try it with my language (Slovene) and am just disappointed. If you claim to support all those languages, please have a sample result in all of them. Even if they aren't all equally good, it comes across as more genuine than making bold claims that anyone who speaks a language with < 10 million speakers knows likely aren't true.
By far the biggest factor seems to be the amount of translated material in that language, followed by how "obvious" the rules of the language are making it easy to decompose algorithmically.