I would try:
(define-abbrev-table 'global-abbrev-table (append tablet1 tablet2))
The point is that the second argument of
define-abbrev-table must be a single list (of two-element lists).
append lets you combine two or more such lists into one by concatenating all the argument lists into one list .
See the doc string of
C-h f append:
append is a built-in function in ‘C source code’.
(append &rest SEQUENCES)
Concatenate all the arguments and make the result a list.
The result is a list whose elements are the elements of all the arguments.
Each argument may be a list, vector or string.
The last argument is not copied, just used as the tail of the new list.
BTW, it is now tested and it works fine.
append actually makes copies of all its argument lists except the last. This is irrelevant for the above discussion, but it is important in general. The last argument is "shared" structure: you can get to it through the
tablet2 variable and also through the result of
append. See the Emacs Lisp manual, section "Building Cons Cells and Lists" for some discussion. You can get to that section with
C-h i g (elisp) RET i cons cells RET.