Simplify polyglossia language loading

See also reutenauer/polyglossia#532 (comment)

.devcontainer/image/acp.cls

@@ -937,23 +937,7 @@
  % secondary language. This is very convenient if for example a thesis is in English,
  % but certain parts have to be in German, e.g. for legal reasons. A simple switch
  % \begin{german} ... \end{german} would then achieve that.
- %
- % Note that we can also do \setotherlanguages{english, german, ...}, for a
- % one-stop-shop, but that would also mean loading the main language as an "other"
- % language, which has "trouble" written all over it. Therefore, choose this weak/
- % somewhat manual approach.
- \iflanguageloaded{english}{%
- \setotherlanguage{german}%
- }{%
- % Nested ifs are ugly, but case-switch is not available and
- % flat, subsequent ifs could load the first language both as a main and
- % as an "other" language
- \iflanguageloaded{german}{%
- \setotherlanguage{english}%
- }{%
- % False: do nothing
- }
- }%
+ \setotherlanguages{german,english}
 
 % Proper quotation support, mainly through \enquote
 \RequirePackage[