Email message content incorrectly displays content for user account's preferred language instead of current site lauguage

[angrybrad]

Description

Default email message content incorrectly displays content for user account's preferred language, instead of the language of the current site.

Steps to reproduce

1. Setup a multisite install with Site 1 (primary site) in French.
2. Add another Site 2 in Dutch.
3. Under your user account preferences, set your language account preference to English.
4. Go to Settings->Email->System Messages.
5. Click to edit the "Activate your account" system message.
6. Notice "French" is selected in the locale selector, but you get the default English content in the body.
7. Add some French content to the body.
8. Save
9. Reopen and notice you still get the default English content, even though your French copy was saved into craft_systemessages successfully.

Additional info

• Craft version: 3.0.16
• PHP version: 7.x
• Database driver & version: n/a
• Plugins & versions: n/a