In 4.0 (and for some time), the credit/debit column headings in the register are untranslated / missing translation. It's only the credit/debit columns, not any other columns.

Turns out these strings come from libgnucash/engine/Account.cpp and there the static variables 

std::map<GNCAccountType, const char*> gnc_acct_debit_strs = {
    { ACCT_TYPE_BANK,       _("Deposit") }, ...

and gnc_acct_credit_strs. The cause of the error is the "static initialization order fiasco" of C++. Now it is ok in C++ to call functions in the initialization of the static variables. However, those function calls apparently occur before the actual translation system has been set up and is pointing to the correct translation catalogs. Hence they just return the untranslated strings, store those in the static variables, and those are never changed again.

My proposed fix: Make the translation in the actual accessor function gnc_account_get_debit_string()  and get_credit_string, and not in the initialization of the static variable.

Sounds ok?