UTF8 encoding and non-text data types

I understand PG supports UTF-8 encoding and I have sucessfully inserted
Unicode text into columns. I was wondering about other data types such as
numbers, decimal, dates

That is, say I have a table t1 with
create table t1 { name text, cost decimal }
I can insert UTF8 text datatype into this table with no problem
But if my application attempts to insert numbers encloded in UTF8, then I
get wrong datatype error

Is the solution for the application layer (not database) to convert the
non-text UTF8 numbers to ASCII and then insert it into database ?

Thanks
Medi