gutenberg_load_plugin_textdomain is looking for an incorrect directory

[strategio]

Issue Overview

In gutenberg_load_plugin_textdomain, the last argument passed to load_plugin_textdomain is pointing to gutenberg/lib/languages/ instead of gutenberg/languages/.

Steps to Reproduce (for bugs)

1. Build the pot file with npm run gettext-strings.
2. Create po and mo files in another language (let's say French => gutenberg-fr_FR.mo) and place the files in gutenberg/languages/.
3. Translate the string "Add block" to "Ajouter un bloc" (this is the first top left corner tooltip for the "+" icon).
4. In your WordPress profile, change the admin language accordingly (i.e. French).
5. Open the Gutenberg editor, and mouse over the "+" icon.

Expected Behavior

=> The tooltip should display "Ajouter un bloc".

Current Behavior

=> The tooltip display "Add bloc" (the string is not translated).

Related Issues and/or PRs

This issue has probably been introduced by #985

[aduth]

Fixed by #5040