In the context in which I had to use an English and French RuleBasedNumberFormat instance, I realized that when parsing numbers followed by units in letters, the default locale is always used and not the one specified in the instance.
The attached file shows a simple test to illustrate the problem.
The workaround is to set the default locale before each parse but this is a bit awkward.
Université de Montréal
The test case fails because I asked Doug to hold the RBNF rule data update. The update of the data is not actually related to this specific problem. So I reopen this ticket and modify the test case based on the current English RBNF rule. John will refactor/refresh the entire RBNF rule data along with the data migration to CLDR.