What online tool do you use to automate translation of .arb files?

Edit (June 2020): There's great new open source project called Arbify. This is a self-hosted tool to manage multiple translation projects focused on Flutter. You can edit arb files and fetch them via Dart package tool.

Aside from that some services like POEditor have announced basic support for ARB too.

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At the moment the best support for arb files is on Localizely. However, this is a paid service and has strict limits on a free version. It allows to export arb translation files with plurals and placeholder support. It doesn't support genders, though.

There is also one simple web editor and one desktop editor (Babel) that support arb files.

Crowdin supports .arb:

https://support.crowdin.com/supported-formats/

It is also able to pull the data from a Git repo and send Pull Requests on GitHub.

However, when I used it in 2018 there was a problem of @@last_modified attribute being updated without any other changes to the translation files, causing lots of churn in PRs. By that time, they were reluctant to improve the situation (based on email conversation with their support), so we resorted to manual edits.