If you have an active user community, and especially if you have people who build consulting businesses around your product, this is a great place to go for linguistic QA help.
Power users who speak other languages will understand your product and the local market better than an agency will. At Notion, we hired power users and consultants who have a background in translation to act as language leads. This made the difference between ok translations and Notion feeling like it was crafted for people in their language.
You can generally expect to pay $40-$75 per hour for this type of service (don’t try to get people to do this for free, as it is difficult to maintain consistency with crowd sourced translations).