Description:
I have installed LibreOffice in German, but - using customized install - also added Dutch / Nederlands as additional language.

Throughout different parts of LibreOffice, some menu items or default document titles are now in Dutch / Nederlands instead in German.

Examples:
Opening up Impress:
-> Dialogue for Templates shows "Openen" and "Annuleren" (Nederlands; WRONG here) and the title of the empty document is "Geen titel 1" (which is also Nederlands; WRONG here).
The menus are displayed completely in German (CORRECT), with exceptions regarding closing LibreOffice ("LibreOffice afsluiten" - Nederlands, WRONG) and saving files: "Datei" (File) menu and Burger menu both include the Nederlands "Opslaan" (WRONG) instead of the German "Speichern" entry. The file menu has a few more of those "opslaan" entries (WRONG), while the ribbon menu displays the correct German "Speichern" and "Speichern unter" (CORRECT).

Steps to Reproduce:
1. Install LibreOffice with custom install. Primary language German, additional language Dutch / Nederlands.
2. Start LibreOffice Impress (or Writer, similar behaviour).

Actual Results:  
see "Steps to Reproduce"

Expected Results:
Localization should have been in German, only, unless explicitly selected otherwise.


Reproducible: Always


User Profile Reset: Yes



Additional Info:
As you can see below, the mixed localization also shows in the "About" dialogue:

Version: 5.4.2.2 (x64)
Build-ID: 22b09f6418e8c2d508a9eaf86b2399209b0990f4
CPU-threads: 4; Besturingssysteem:Windows 6.19; UI-render: standaard; 
Gebietsschema: de-DE (de_DE); Calc: group




User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:56.0) Gecko/20100101 Firefox/56.0