There are many ways you could achieve this. First is yes, you could add the html tags within the translation file.
Another solution would be to use a helper for this. Helpers are meant to help view creation. Within your helper file, you could define the following method
def bolded_translated_test
t('test', another_variable: "<b>#{t('another_variable')}</b>"
end
Then in your view, you can use it
<%= bolded_translated_test %>