The first recommendation is Lernu because this website provides many instruction languages including Bahasa Indonesia and English so whatever your mother language, you won’t be missed.
Second recommendation is Duolingo. If you are native Indonesian, it has the instruction language. However, but it looks like the translator of this website is not a native Indonesian so some of paragraphs were rather confusing.
If you have already fluent in English, the third recommendation is Edukado.
The Google Translation is not a learning site, but you can easily find the definition on many languages, including Bahasa Indonesia, English and Esperanto. It can help if you want to verify whether your sentence is already correct.
Google Translator – English Esperanto