What are some alternatives?
When comparing Protranslate and GTS Translation, you can also consider the following products
OneSky - Full Stack Localization Solution
One Hour Translation - Professional translation services for 75 languages on a 24/7 basis.
Crowdin - Localize your product in a seamless way
Gengo - People-powered translation at scale.
Zanata - Homepage for Zanata translation software
Localization Guru - Professional translation services for 65+ languages with 48-hour delivery.