YOU SAID:

translation in general is a very tough nut to crack

INTO JAPANESE

かなり堅牢だ

BACK INTO ENGLISH

It's quite robust

INTO JAPANESE

それは非常に堅牢です

BACK INTO ENGLISH

It is very solid...

INTO JAPANESE

それは非常に強固.

BACK INTO ENGLISH

It is very solid.

INTO JAPANESE

それは非常に強固です。

BACK INTO ENGLISH

It is very solid.