We cannot know too much about our own language.
The JP-EN pair doesn’t match.
自国の言葉 means “all languages spoken in one’s home country.”
Suppose that the speaker is from India, his mother tongue is Tamil, and he doesn’t speak other languages.
If he says 自国の言葉, the phrase refers to at least two federal official languages: Hindi and English, or it may do so 22 regional official languages.
However, “our own language” in the English sentence refers to Tamil only.