Is translating advertisements that may be used for car loudspeakers – which are often used for music – considered a sin? And what is the ruling on advertising devices that can be used for both a permissible and a forbidden purpose?

It is permissible to buy and sell what is used for both lawful (mubah) and unlawful (haram) purposes if it is highly probable that it will be used for lawful purposes. However, it is forbidden to sell it if it is highly probable that it will be used for unlawful purposes. If the buyer's intention is unknown, then the sale is permissible. Thus, what is forbidden is selling to someone who is known or highly likely to use the item for impermissible purposes. As for advertising these goods, it is permissible because it is a general announcement and not directed at a specific buyer.