The language code for Hinglish is "hi-t-en-h0-hybrid". The name for that should be "Hindi (Hinglish)" (and the equivalent in Hindi), but we don't have structure for that. This is not an isolated example: we need to prepare for additional forms such as "ta-t-en-h0-hybrid" ==> "Tamil (Tanglish)"
What we do have is
<key type="h0">Mixed-in Language</key>
<type key="h0" type="hybrid">Hybrid Language</type>
But we don't have the spec for how to handle 't' properly. My proposal is to add the following language to the spec (plus a new element).
== Spec addition ==
If the extension is 't', then the t extension language (eg "en") is formatted and added to the parenthetical. For example:
"hi-t-en-h0-hybrid" ==> Hindi (English, Hybrid)
"de-t-en-h0-hybrid" ==> German (English, Hybrid)
The other language subtags are also used. This is for completeness; unlikely to occur in practice.
"de-AT-t-en-GB-h0-hybrid" ==> German (Austria, English (UK), Hybrid)
If there is a <hybrid> element, then it is used to produce a combined form. The language is formatted as usual, but the language subtag plus the t extension language subtag are mapped together to get a replacement name for the t extension language subtag.
For example, assume we have <hybrid target="hi" source="en">Hinglish</hybrid>. Then:
"hi-t-en-h0-hybrid" ==> Hindi (Hinglish)
Similarly, other language subtags are added as in (a). Again this is for completeness; unlikely to occur in practice.
"hi-SG-t-en-US-h0-hybrid" ==> Hindi (Singapore, Hinglish (US))
ICU ticket filed as https://unicode-org.atlassian.net/browse/ICU-20405
== Data Changes ==
1. modify en.xml
<type key="h0" type="hybrid">Hybrid</type>
<hybrid target="hi" source="en">Hinglish</hybrid>
2. add the equivalent for Hindi:
// the following are examples and would need to be vetted//
<type key="h0" type="hybrid">संकर</type>
<hybrid target="hi" source="en">हिंग्लिश</hybrid>
In preparing for the next release:
3. make h0 be coverage = modern
Document how it is used and provide example. Depending on the language, "hybrid" might be something like "mixture" or "combined", etc.