Then word for language is gengo (言語). Most of the time the word for a language is the country name and the word go (語) attached the end, however there are some exceptions.
English = eigo (英語)
Japanese = nihongo (日本語)
Arabic = arabiago (アラビア語)
German = doitsugo (ドイツ語)
Russian = roshiago (ロシア語)
Chinese = chuugokugo (中国語)
Spanish = supeingo (スペイン語)
Japanese is the official language of Japan. English is taught in schools as a second language; however the amount of Japanese people who can speak it is less than 1%. Even though you will find other languages on signs around Japan, it is very difficult to make your way around without knowing at least basic Japanese.
The verb hanasu (話す) means To speak.
(I) speak English = eigo o hanashimasu (英語を話します)
(I) speak English = eigo o hanasu (英語を話す)
Reminder: Both sentences mean the same thing, masu form is polite.
She speaks French and Spanish = kanojo wa furansugo to supeingo o hanashimasu (彼女はフランス語とスペイン語を話します)
Do you speak Chinese? = chuugokugo o hanashimasu ka
Wakaru (分かる) is a verb that is used to mean both to know & to understand. It's translation depends on the sentence it's in.
(I) don't know the meaning = imi wakaranai (意味分からない)
Do you understand? = wakaru? (分かる？)
It's not uncommon for a language learning in Japan to have a Electronic dictionary denshi jisho (電子辞書). Some of them are pretty high tech and can cost hundreds of dollars. The word for dictionary is jisho (辞書)