How to resolve i8n messages of other plug-ins

How can we resolve i8n messages of other plug-ins from our plug-in?

com.atlassian.sal.api.message.I18nResolver i18n = ...
String key = "bitbucket.automerge.conflicted.pull-request.title";
String text = i18n.getText(key);

where that key is defined on bitbucket-branch-7.21.7.jar!/i18n/bitbucket-branch.properties.
Thanks in advance.
Cheers.