You are welcome. Notice that I was not being pedantic when I referred that it was not a false friend.
If you try your rule in a German text, you will be overwhelmed by spelling errors. If you set your text to English and place this rule in the German grammar.xml, the rule will not trigger.
Some languages have a category equivalent to 'Translation Errors'. This rule would fit there (if localized to the target language, English in this case).
False friend structure is:
<pattern lang="XX"><!-- translated language code -->
<translation lang="de">false-friend translation</translation>
<pattern lang="de"><!-- your language -->
<token inflected="yes">German word similar to the false-friend</token>
<translation lang="XX">translation to target language</translation>
This is a good place to start:
Just clean the table in Calc/sed/Notepad++ and make a few replacements/greps to get a nice list in instants. The tough part is triaging, finding duplicates and placing the lines in the right place, but it is a great help.
At least, I would thank if you decide to improve German-Portuguese pairs.