Spelling aside French isn’t really more difficult than Spanish. Neither language is terribly difficult when you compare it to Hebrew, Arabic, Russian or Japanese but German grammar is definitely more complex than French and that’s where most of the difficulty is in Category 1 and 2 languages, not the phoneme inventory or vocabulary, with their masses of cognates with English.

Due to the Norman conquest of England in 1066 there's a good chunk of vocabulary overlap, particularly for the more formal and technical words likely to be used in State Department contexts.