It depends on your target language and your definition of converse well. Under the Common European Framework of Reference for defining language ability, B2 (upper intermediate) is the level at which speakers can use a language for social and professional purposes without causing "undue strain on other parties." B2 isn't the maximum level, but it is the minimum level most people mean when they say fluent. It's possible to 'converse well' at lower levels. B1 (Intermediate) is the first level at which learners are considered to be independent users of their target language. They can handle everyday tasks in the target language, but may use the language inappropriately because they don't yet have a nuanced understanding of the language or culture. Users at this stage can interact with native speakers in a limited way, but will be lacking large chunks of the vocabulary and lexis needed for accurate interactions which do not cause strain for native speakers. Cambridge University's ESOL department tells us that most foreign students of English will need approximately 650 hours of classroom instruction + homework to reach B2. B1 is attainable in 450-550 hours of instruction. The US military, which trains intelligence officers in foreign language, provides data similar to these values. The US military says that Spanish, French, Italian, Romanian, Dutch, Norwegian, and Swedish are easy languages for a native English speaker. German and Russian are significantly more difficult to learn. Georgian, Turkish Arabic, and Mandarin Chinese are rated as difficult languages to learn for a native English speaker. Japanese and Korean are rated as extremely difficult for a native speaker of English to learn.