Full preprocessor support in Inno Setup language files (isl) - inno-setup

Question

I use three languages with my installer and at the moment I'm doing all the overrides inside my script. Here's an example:
[Messages]
en.SetupWindowTitle=Setup - %1 {#AppVersion}
ru.SetupWindowTitle=Установка - %1 {#AppVersion}
ua.SetupWindowTitle=Встановлення - %1 {#AppVersion}
en.SetupAppRunningError=Setup has detected that {#SetupSetting('VersionInfoOriginalFileName')} is currently running.%n%nPlease close all instances of it now, then click OK to continue, or Cancel to exit.
ru.SetupAppRunningError=Обнаружен запущенный экземпляр {#SetupSetting('VersionInfoOriginalFileName')}.%n%nПожалуйста, закройте все экземпляры приложения, затем нажмите «OK», чтобы продолжить, или «Отмена», чтобы выйти.
ua.SetupAppRunningError=Виявлено запущений екземпляр {#SetupSetting('VersionInfoOriginalFileName')}.%n%nБудь ласка, закрийте всі копії програми та натисніть «OK» для продовження, або «Скасувати» для виходу.
[CustomMessages]
en.AppRunningError=Setup has detected that {#AppExeName} is currently running.%n%nPlease, close the {#AppExeName} application, then click «OK» to continue or «Cancel» to exit.
ru.AppRunningError=В памяти находится {#AppExeName}.%n%nЗавершите работу {#AppExeName} и нажмите «OK», чтобы продолжить, или «Отмена», чтобы выйти.
ua.AppRunningError=В пам'яті знаходиться {#AppExeName}.%n%nЗавершіть роботу {#AppExeName} та натисніть «OK» для продовження, або «Скасувати» для виходу.
I have lots of messages overridden inside the script. I would like to know what is the most effective way to transfer all those overrides into the .isl files taking into account that I have preprocessor directives {#...} used. I could use FmtMessage(...), but that means that I would have to include FmtMessage(...) for every single message.

Answer 1

First check, if some of the less invasive solutions might not cover your needs:
Can I use .isl files for the messages with preprocessor directives in Inno Setup?
If you want a full preprocessor support in .isl files, you can pass them through the actual Inno Setup preprocessor:
Factor out common include file (defines.iss) with all the variable definitions (and some support code):
// Definitions
#define AppVersion "1.2.3"
// more definitions ...
// Support code
#define PreprocessedTranslationFile GetEnv("TEMP") + "\lang.isl"
#define SavePreprocessedTranslation() SaveToFile(PreprocessedTranslationFile)
Include that file at the beginning of your .iss and all your .isl's:
#include "defines.iss"
Call SavePreprocessedTranslation at the end of all your .isl's:
#expr SavePreprocessedTranslation()
Make the preprocessor call iscc on the modified .isl files. It will of course fail, as the .isl is not a valid .iss, but the preprocessor part of iscc should complete and create the preprocessed .isl file.
#define DebugPreprocessLanguage 0
#define PreprocessLanguage(Path) \
Local[0] = "C:\Program Files (x86)\Inno Setup 6\ISCC.exe", \
DeleteFileNow(PreprocessedTranslationFile), \
Local[1] = DebugPreprocessLanguage ? SourcePath + "\islpreprocess.log" : "nul", \
Local[2] = "/C """"" + Local[0] + """ """ + Path + """ " + \
">> " + Local[1] + " 2>&1 """, \
Exec("cmd", Local[2], SourcePath, , SW_HIDE), \
(FileExists(PreprocessedTranslationFile) || \
Error(Path + " failed to preprocess")), \
Local[3] = GetEnv("TEMP") + "\" + ExtractFileName(Path), \
CopyFile(PreprocessedTranslationFile, Local[3]), \
DeleteFileNow(PreprocessedTranslationFile), \
Local[3]
And use the preprocessed .isl files in the [Languages] section.
[Languages]
Name: "en"; MessagesFile: {#PreprocessLanguage("Default.isl")}
Name: "nl"; MessagesFile: {#PreprocessLanguage("Dutch.isl")}
If you have problems, set DebugPreprocessLanguage to 1 to see the .isl preprocessor output.
You can even improve the process by making the preprocessor add the #include "defines.iss" and #expr SavePreprocessedTranslation() automatically to the .isl's before calling the iscc.