In French, the word for soda is « soda » or sometimes « une limonade » depending on the context. The term « soda » is used quite widely and is understood to refer to carbonated soft drinks.
When ordering in a café or restaurant in France, you might say, « Je voudrais un soda, s’il vous plaît », which means « I would like a soda, please ». On the other hand, « limonade » might refer specifically to lemon-flavored soda or a type of carbonated soft drink.
Understanding the context is important, as regional variations can exist. In casual conversation, most people will understand what you mean by « soda ».