In fact, the “dialects” of what we think of as the “languages” of French, German, and Spanish are more different than the dialects of English. The reference I’m going to be using for this post is Ethnologue. It’s a good but not perfect source on the languages of the world. In particular, it tends to be more of a splitter than a lumper. That is, it tends to divide the varieties of language in the world into separate languages a little more than some linguists would, so things that some people think of as just dialects are listed as being different languages in Ethnologue.
Here’s what it says on the varieties of English:
In other words, the only two separate languages of what we think of as English are Scots, spoken in parts of Scotland, and English, spoken in all the rest of the English-speaking world.
Here’s what it says on the varieties of French:
In other words, it thinks the varieties of French spoken around the world are different enough to be broken into five different languages, one of which is the language we think of as French.
Here’s what it says about the varieties of German:
In other words, there are two groups of languages. One is the group of nineteen High German varieties. The other is the group of ten Low German varieties. It considers these to be different enough that there are nineteen German “languages.”
Here’s what it says on the varieties of Spanish:
In other words, it considers that there are four different languages among the varieties of Spanish.
And there are varieties of languages spoken in France, Germany, and Spain that are sometimes thought of as being French, German, or Spanish but which are even further from what we think of as those languages.
So the differences between what we think of as dialects of French, German, and Spanish are clearly bigger than the differences between what we think of as dialects of English. Is this enough to convince you that this is an incredibly difficult issue? What you want to call a dialect and what you want to call a separate language is a hopelessly complex matter.