IsMailEuropean → ParseMailLanguage (and give it constants)

constants/item_data_constants.asm

@@ -59,6 +59,14 @@ DEF MAILBOX_CAPACITY      EQU 10
 DEF MAIL_STRUCT_LENGTH    EQU $2f ; mailmsg struct
 DEF MAIL_STRUCT_LENGTH_JP EQU $2a ; mailmsg_jp struct
 
+; mail languages
+	const_def
+	const MAIL_LANG_ENGLISH
+	const MAIL_LANG_FRENCH
+	const MAIL_LANG_GERMAN
+	const MAIL_LANG_ITALIAN
+	const MAIL_LANG_SPANISH
+
 ; held item effects
 	const_def
 	const HELD_NONE

constants/serial_constants.asm

@@ -30,15 +30,16 @@ DEF SERIAL_PATCH_LIST_PART_TERMINATOR EQU $ff
 ; used to replace SERIAL_NO_DATA_BYTE
 DEF SERIAL_PATCH_REPLACEMENT_BYTE     EQU $ff
 
-DEF SERIAL_PREAMBLE_LENGTH            EQU 6
-DEF SERIAL_RN_PREAMBLE_LENGTH         EQU 7
-DEF SERIAL_RNS_LENGTH                 EQU 10
+DEF SERIAL_PREAMBLE_LENGTH    EQU 6
+DEF SERIAL_RN_PREAMBLE_LENGTH EQU 7
+DEF SERIAL_RNS_LENGTH         EQU 10
 
-DEF SERIAL_MAIL_PREAMBLE_BYTE         EQU $20
-DEF SERIAL_MAIL_REPLACEMENT_BYTE      EQU $21
-DEF SERIAL_MAIL_PREAMBLE_LENGTH       EQU 5
+DEF SERIAL_MAIL_PREAMBLE_BYTE    EQU $20
+DEF SERIAL_MAIL_PREAMBLE_LENGTH  EQU 5
+; used to replace SERIAL_NO_DATA_BYTE
+DEF SERIAL_MAIL_REPLACEMENT_BYTE EQU $21
 
 ; timeout duration after exchanging a byte
-DEF SERIAL_LINK_BYTE_TIMEOUT          EQU $5000
+DEF SERIAL_LINK_BYTE_TIMEOUT EQU $5000
 
-DEF MAX_MYSTERY_GIFT_PARTNERS         EQU 5
+DEF MAX_MYSTERY_GIFT_PARTNERS EQU 5