When running Magnolia on a system with system locales differing from Locale.ENGLISH one might end up with scenarios where translations provided by new and old translation system come from different languages. See

So even though current use (here superuser) has the locale set to English in his settings, one of the legacy translations shows up in the system locale (which was de_CH.UTF-8, or simply de). Additionally those translation might show up with encoding errors due to being read without UTF-8 but rather ISO-8859-1.

Source of the problem

So when no bundle matching Magnolia file naming convention is found, the following line info/magnolia/cms/i18n/DefaultMessagesImpl.java:106 will fallback to Java's bundle loading:

bundle = ResourceBundle.getBundle(getBasename(), locale);

Java's messages properties file a read with ISO-8859-1 character encoding by default, see link below. Additonally the Locale is detected from the system, resulting in more issues.

(..) The input stream is in a simple line-oriented format as specified in load(Reader) and is assumed to use the ISO 8859-1 character encoding; (..)