What are some alternatives?
When comparing Transifex and Crowdin, you can also consider the following products
POEditor - The translation and localization management platform that's easy to use *and* affordable!
Smartling - Website localization & translation
Lokalise - Localization tool for software developers. Web-based collaborative multi-platform editor, API/CLI, numerous plugins, iOS and Android SDK.
OneSky - Full Stack Localization Solution
Weblate - Weblate is a free web-based translation management system.
Memsource - Manage your translation workflow more efficiently with Memsource.