Encoding error in error messages #459

Steps to reproduce

1. Login as a user in Firefox
2. Switch language to "French"
3. Go to Files app and drag&drop a folder

Expected behaviour

Error message should appear properly in the interface.

Actual behaviour

Encoding of the message is broken. Screenshot:

A OC 8.2.7 setup on the same system doesn't show this problem.

Server configuration

Operating system: Debian 8

Web server: Apache

Database: MariaDB

PHP version: php7.0 (dotdeb-packages)

Nextcloud version: 9.0.53

Updated from an older Nextcloud/ownCloud or fresh install: 9.0.52

Signing status: no error.