Erratic foreign language
Foreign words or sentences are thrown in the dialogue or writing seemingly randomly, or are used inexplicably with some things such as describing technology.
Alternate name: Flavour foreign language
The first video game about Erratic foreign language was released on October 30, 1998.
This is not about characters speaking their native tongue as usual, but rather those languages surfacing in speech in another. Although commonly heard with "foreigners" reverting to their native tongue for exclamations, curses, and other abrupt/unplanned statements, this tag is more about when it's done on purpose.
Also this should not include mixed language when it's normal for the region or language, for example English has many commonplace French, Latin, Spanish, and other loan words and expressions that are out of place for this tag.