Probably Mandarin Chinese.
Languages that are often considered to be the most complicated include languages with highly elaborate grammar systems, such as Basque, Icelandic, and Korean. Additionally, languages with complex writing systems, such as Mandarin Chinese or Japanese, can also be seen as challenging due to the need to learn thousands of characters. However, the difficulty of a language can also depend on the learner's native language and personal experience.
books, the Internet and most importantly YOUR WILL to learn no matter how hard or complicated it can be good luck
Languages like Mandarin Chinese, Arabic, and Russian are often considered among the most complex to learn due to their unique writing systems, grammar structures, and pronunciation challenges. Language complexity can vary depending on an individual's native language and learning experience.
English
Most of Indonesian learn Indonesian language as second language aside of their local regional language.
Most Brazilians, like most other people, don't go anywhere to learn their native language. They learn it at home as infants and young children.
the most widely spoken language is english so that is good to learn if you don't know it already. spanish is also a good language to learn because it is common and the most people on earth speak chinese so that is also good.
The best language to learn singing in Europe is English because it is the world's most spoken language.
hindi
You can learn a slavic language online by using the slovio site or the multilinguals website. Most of the available options are not free and they usually connect you with a personal tutor who will help you to learn the language.
Because finance itself can be quite complicated, most software about it will seem complicated. However, a good program will provide good instructions for use and an easily accessible help option on most if not all pages. So no, it should not be hard to learn.
Most experts believe immersion is the fastest way to learn any language.