This extension allows to get language labels from ext:translatr as JSON.

Use composer:

composer require sourcebroker/t3apitranslatr

After installing the labels are accessible by following endpoint: /_api/translations

To narrow the number of labels fetch you can use tags on ext:translator and get only those tags that are needed on page.

/_api/translations?tags[]=general&tags[]=user

See https://github.com/sourcebroker/t3apitranslatr/blob/master/CHANGELOG.rst