The 2th sentence in De Bello Gallico Liber I.
Hi omnes lingua, institutis, legibus inter se differunt.
The word lingua is put Ablative Singular. Why?
I am not a native speaker of Indo-European languages. It is hard for me to understand how one language can differ from each other (inter se differunt).
And the following 2 words are put in Ablative Plural. Only lingua is put in Ablative Singular.
In Latin, like in English, "language" is sometimes treated as an uncountable thing (a "mass noun"). When linguists study "language", it doesn't mean they study only a single language; it's like how "water" can mean either a specific body of water (with the plural "waters"), or the substance of water in general (with no plural).
In other words, the different Gallic tribes differ from each other in their systems, laws, and language. That's a fairly natural way to phrase it in English; you could also say they differ in their law rather than treating the laws as specific concrete things, but this is less common.
