English

Around 380 million people speak English as a first language and another 750+ million speak it as a second language, putting total speakers above one billion. It's the official or working language of more countries and international bodies than any other.

English is a West Germanic language, the same branch as Dutch, German, Frisian, and Yiddish. Going further out it's Indo-European, so it shares deep roots with Spanish, Russian, Hindi, and most languages of Europe. Old English looked far more like modern German before centuries of contact with French and Norse reshaped it.

The spelling froze around the time printing took off in the 15th century, just as the Great Vowel Shift was changing how words were pronounced. Add layers of French, Latin, and Greek borrowings that kept their original spellings, and you get knight, though, queue, and choir all coexisting.

No. English lost its three-gender system around the 12th century. The only real gender survival is in pronouns (he, she, they, it). Nouns and adjectives have no gender agreement, which is one reason English is structurally simpler than its Germanic and Romance neighbours.

It depends what you start from. Speakers of other Germanic and Romance languages get a lot for free. The grammar is light on inflection. The hard parts are the irregular spelling, the dense system of phrasal verbs (look up, look out, look after), and the reliance on stress and rhythm that learners often miss.