What are some alternatives?
When comparing Pootle and Transifex, you can also consider the following products
Crowdin - Localize your product in a seamless way
Poedit - Poedit translations editor. The best way to translate apps and sites.
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Smartling - Website localization & translation
Weblate - Weblate is a free web-based translation management system.
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.