What is the ruling on Zakat for money invested in a translation office? Is it obligatory only on the principal capital, or on both the principal capital and the profit, especially since the beneficiary is left with nothing from the profit and principal capital after covering his needs and debts?

There is no Zakat (definition) on capital invested in a translation office if it is used to purchase equipment and rent the premises, because it is considered an asset from which income is derived (mustaghallat). Zakat is due on the income (ree') if it reaches the nisab (definition) and a full year has passed over it. If the income does not remain for a full year and is spent on expenses, then there is no Zakat on it either.

The partnership between you and your partner is a Mudarabah (definition) partnership, where you contribute only capital while your partner contributes both capital and labor. This partnership can be a combination of a Musharakah (definition) al-Inan and Mudarabah, especially if one partner works without the other. In this case, it is stipulated for the one who exerts physical effort to receive a larger share of the profit than the profit from his capital.