Hi there,
in my opinion, it's better to use 2 separate domains, because you want that to get the most impact from the SEO performance of your website, right?
Because if you would make a multilingual website, you would have to use Keywords in 2 or more languages, which has a lower impact for your SEO performance, than using more Keywords, but only in one language, which generates much more local attention on your website. Furthermore, it's also the viewers, which still would get to your website, because they might be get distracted by the content, because they don't understand everything, which would let to a higher bouncing rate on your page, which can also affect negatively on the ranking of your page. That's why I personally would use 2 or more domains.
Yes, it means that you have to do the double, triple amount of SEO work for, but it also has the double, triple amount of impact on your business.
regards,
Jürgen