The term for soy sauce in Spanish is salsa de soya. In some regions, it might also simply be referred to as salsa de soja. Both terms are understood in Spanish-speaking countries, but salsa de soya is the more commonly used phrase.
When you visit a restaurant or a grocery store in a Spanish-speaking country, using salsa de soya will generally allow you to communicate your needs effectively. It’s always helpful to understand local variations in names, as some regions have their own favorites!