What are some alternatives?
When comparing Transifex and Smartling, you can also consider the following products
Crowdin - Localize your product in a seamless way
POEditor - The translation and localization management platform that's easy to use *and* affordable!
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
Localize - Localize is translation software that automatically converts the content of your website or app into multiple languages.
Weblate - Weblate is a free web-based translation management system.