Tax Rule descriptions can not be translated:

'This Tax Rule is to be used when a product is not subject to sales tax. Thus no Tax Rates can be assigned to this rule, which can not be edited, nor deleted.'

Missing:

'No taxes'
'Not subject to sales tax'


Main Page of Tax the whole description is not translated:

Here is how taxes work:
a Product Plan can get assigned a Tax Rule
a Tax Rule can get assigned several Tax Rates (e.g. Canada needs multiple ones: country and state taxes apply)
a Tax Rate defines a tax %, and depends on a Geographic Zone
a Geographic Zone is comprized of Geographic Zone Entries
a Geographic Zone Entry is a Country and optionally a Province/State
Thus, when a buyer billing addres is in a given Geographic Zone which has Tax Rate(s) assigned to a Tax Rule used by a Product Plan, the corresponding invoice item computes the corresponding tax that is added to the invoice.