How to say you had better get this letter registered for fear it should be lost. in Japanese
1)
このこの(kono) (n) this手紙手紙(tegami) (n,adj-no) letterはは(ha) (int) indicating a subject/yes/indeed/well/ha!/what?/huh?/sigh紛失紛失(funshitsu) (n,vs) losing somethingするとすると(suruto) (conj) thereupon/hereupon行けno dictionary result, likely a conjigated verbno dictionary result, likely a conjigated verbないない(nai) (aux-adj) not/emphatic suffixからから(kara) (prt) from/since/from/because/out of/through/after/since、、(、) Japanese comma書留書留(kakitome) (n,vs,adj-no) registered mail/registration/writing down/putting on record/recording/making a note ofにに(ni) (prt) indicates such things as location of person or thing, location of short-term action, etc.するがよいするがよい(surugayoi) (exp) had better .../may as well ...。。(。) Japanese period "."
