The speaker's argument rests entirely on saving taxpayers' money: printing documents in many languages is a waste, so Hindi alone should be the official language. To weaken this the most, an option must attack the "wasted taxpayer money" reasoning itself, ideally by showing that the very people being asked to switch to Hindi are the ones funding the government in the first place.
Only the tax-paying option cuts at the reason the speaker actually gives, wasted taxpayer money, so it weakens the argument the most.
Let's summarize:
So the correct option is "People who are multilingual usually pay the maximum taxes."