According to the US Foreign Service Institute and many others, (for native speakers of English) it's about the same as Spanish, Romanian, Italian, Portuguese, Catalan, Swedish, Norwegian, Danish, Dutch, Frisian and Afrikaans.

The only sizable language that's significantly easier to learn is Esperanto

According to the US Foreign Service Institute, it will take a native speaker of English, already fluent in a second language, some 600 hours of class (that's 24 weeks minimum) to get fluent in an easy language such as Norwegian.

the only sizable language that can be learned significantly faster is Esperanto

zirp  zirpenstein  answered 3/31/2016

According to the US Foreign Service Institute, an already bilingual native speaker of English with an adult vocabulary will need 2200 hours of class, so at least 88 weeks,  to get fluent in Mandarin (or any other of the sinitic languages)

According to the US Foreign Service Institute, an already bilingual native speaker of English with an adult vocabulary will need 2200 hours of class, so at least 88 weeks,  to get fluent in Mandarin (or any other of the sinitic languages)