Feature request

Please allow non ASCII but printable characters in ID field.
We, Japanese GTFS engineers, often use some local characters as an ID in order to ease to check the GTFS data by the non-tech person in a transit agency. Especially, we use Japanese expression of types of days such as holiday, weekday in Japanese way in service_id like "平日", "土休日". I think only a machine refers ID as an internal identifier, so even non ASCII characters are usable.

Is your feature request related to a problem? Please describe.
#712 is discussing this issue.
Also, discussion in GTFS specs relate to this issue.

Proposed solution
Remove this rule, or set the category of this rule be "INFO" rather than "WARNING".

Describe alternatives you've considered
One possible solution is to enable this rule referring to the given country code.