What are some alternatives?
When comparing Protranslate and Transifex, you can also consider the following products
OneSky - Full Stack Localization Solution
Crowdin - Localize your product in a seamless way
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Smartling - Website localization & translation
Zanata - Homepage for Zanata translation software
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.