In some cases I need multiple languages in the same LyX document (e.g. when quoting an English text in a German document) and would like to have correct spell-checking for both parts.
LyX apparently supports multiple languages in a document to some degree, because copy-pasting text between documents of different languages results in some blue-underlined text with the different language being set. In LyX's internal format, this is represented by a structure like
This is English. \lang ngerman Hier wird es deutsch. \lang english And german again.
and once such multi-lingual content has appeared in the document, language settings become available in the Edit menu.
When removing the mixed language parts, the menu vanishes again, and thus I cannot find any method to add foreign-language content to a previously single-language document, without the inconvenient copy-paste workaround.
Is there some better way to mark some words as foreign-language?