In German the adverb is the same as the adjective root. No extra ending at all. In Swedish it is "-t", except when a word ends with a "d", in which case it becomes two "t"s, and just after the 1906 spelling reform. Simple and understandable. In English the "-ly" can either miss completely, like in "fast" or you can add something that doesn't belong there at all, like in drastically. Of course it should be "drasticly", if English were one whit logical.
Another illogical thing is the capitalization of "I", names on days, months, officials (the President) etc. In German nouns are capitalized. Period. In Swedish proper nouns (names) are capitalized. Period. German and Swedish have a perfectly logical capitalization, English has an arbitrary.