What are some alternatives?
When comparing Protranslate and Pairaphrase, you can also consider the following products
OneSky - Full Stack Localization Solution
Crowdin - Localize your product in a seamless way
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.
Zanata - Homepage for Zanata translation software
Qordoba - Manage text like code
Poedit - Poedit translations editor. The best way to translate apps and sites.