It's an easy thing to overlook: a guest who can't confidently read your menu doesn't ask more questions - they just order less. Maybe a starter and a drink instead of a full meal, or the one dish they recognize instead of the one your kitchen is actually proud of.
The "safe choice" problem
When guests aren't sure what a dish contains, they gravitate toward whatever sounds familiar - which is rarely your most interesting or highest-margin item. Translating the full menu, including descriptions and not just dish names, removes that hesitation.
Descriptions do more work than names
A dish name alone rarely sells a dish - "Pljeskavica" tells a local everything and a visitor nothing. A short, translated description ("grilled minced-meat patty, served with kajmak and flatbread") does the selling a waiter would otherwise have to do table by table.
It also respects the guest's time
Guests who have to photograph a menu and run it through a translation app on their phone are guests who are distracted, slower to decide, and more likely to just order the first thing they understand. A menu that already speaks their language keeps the whole table moving toward ordering, not toward Google Translate.
Where to start
You don't need every language at once. Start with the one or two languages your actual guests speak most - a tourist-area restaurant might add English and German before anything else, while a delivery-focused spot in a mixed neighborhood might prioritize the languages of the neighborhood itself. The point isn't covering every language in the world; it's making sure the guest in front of you isn't guessing.