Hello, thank you for reaching out regarding this edit.

1. The Names -> Good Practice -> Multiple Names covers this to some extent.

"Sometimes name=* itself can contain multiple values separated by semicolons:

In multilingual regions or localities, multiple names in different languages may be relevant enough to include in name=*. A separator other than a semicolon, such as "/" or "-" (spaced or not), may be customary locally. This is not a substitute for language-specific keys, such as name:en=* for English."

https://wiki.openstreetmap.org/wiki/Names#Multiple_names

A decision therefore needs to be made whether each name is relevant enough to be added with a separator slash such as a "/". One should also take into account whether that language is used by a significant amount of people in that locale.

This goes back to the Ground Truth policy:

https://wiki.openstreetmap.org/wiki/Ground_truth

2. This would go back to coverage in #1. Does it appear on signage and print materials? Is it used locally in equivalent quantities to the English language name? Do a significant portion of the local population speak the language?

Traditional importance would not be a consideration. However, you are welcome to open a discussion topic on the OpenStreetMap Community Forum to gauge opinion from the OpenStreetMap community. What would then follow is a formal proposal on included traditional importance as a qualifer for the OpenStreetMap community to vote on.

https://community.openstreetmap.org/

3. I mentioned this due to a few cases:

#1 An International editor edited Indian Reservation boundaries to include dual Indigenous / English language names. However, the Indigenous name is not an officially recognized or locally used name for the Indian Reservations boundaries. For example, in evacuation notices distributed by the Indigenous band the English name was the name used. In some cases, the Indigenous language is not fluently spoken by more than a handful of people.

#2 The addition of the Indigenous / English language name to Whistler and Britannia Beach in particular. Both of these areas are disputed by Indigenous bands. The Whistler name chosen differed than the name shown on some MOTT signage. But most importantly, neither name is frequently used by a significant portion of locals and hence fails the test to be included in the default name tag.

#3 A recent edit of The Lions peaks to an Indigenous-English version of the name. The Indigenous name is not the official name, not on signage, and not frequently used by locals. 

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My opinion is that some areas like Squamish are borderline cases. The Indigenous name is frequently on signage. The Indigenous name is frequently used on print materials. However, there are only 25 fluent speakers (Statistucs Canada 2021) of the Squamish language and most people would not say the Squamish name in person. This is why that place is a borderline case. 

I recommend starting by opening a discussion topic on the OpenStreetMap Community Forum. This is the best place to get opinion from experienced OpenStreetMap editors and Data Working Group members. This would be the best avenue to get a better understanding of the dual naming standard and to gauge what qualifies.

https://community.openstreetmap.org/

I should also end this my noting that most applications that use OpenStreetMap data default to using the name:en tag. This is therefore largely an exercise in deciding what should show up in OpenStreetMap's default carto rendering, a system that is mainly used as a debugging and testing platform for OpenStreetMap editors.