Ericsson RX8000 Series Reference Manual page 235

The non-ISO languages allow tagging of audio without reference to specific
languages. The system can then transmit two languages (Main and Auxiliary) which
could be any type of audio.
Note:
For language codes not supported by the RX8000 Receiver, the Receiver will list
'undefined' as the language descriptor. This does not affect the way the audio is
selected.
EN/LZT 790 0005 R1A
The non-ISO languages need to be user-defined in the Encoder for them to
be available.
Annex C
C-5