Constant revision helps to retain memory

I am interested in languages. To date, I can speak and write three languages fluently. They are Malay, English and Mandarin. Recently, I have grown to love Japanese. Initially I managed to recognise the 30 or so sounds needed to form Japanese words. Now

I seem to have difficulty in recognising many of them. It shows that constant revision is needed to recall words in any language. The grammar in Japanese is different from that in English. In English, a sentence consists of Subject (S), Verb (V) and Object (O). For example: I read a book. (I=S, read=V and a book=O)

In Japanese, a sentence consists of SVO. The following sentences show this sentence structure:
1 Kore wa neko desu. [This is a cat. neko=cat kore=this desu=is wa=subject marker]
2 Kore wa inu desu. [This is a dog. inu=dog]