Unfortunately Arduino IDE 1.8.4 is not working with the new release of Mac OS High Sierra today. The IDE starts properly, shows recently opened programming windows incl code, but in the top menu bar it only shows the entry "Arduino". There is literally no main drop down menu to choose. You even cant quit the app, you have to force quit it. Though the recently opened fragments of code can be build.
Solved the issue for now. I am using the german language entry (both: primary language and region). When you switch to english primary and region US the menubar appears... Not really a good solution, but it works.
the developers are definitely taking it seriously and have been working on it but have not found a solution. I think the current hope is that Apple will fix this issue before the release.
Here is the workaround from Github which also works for me. I added "German" in step 6 because it was not clear where to paste. Adjust your language as needed. I also modified step 9 to restore system security
Shutdown your Mac
Start in recovery mode and open the terminal then, type "csrutil disable" (else you can't write in the /System folder)
Restart
Go to "/System/Library/Frameworks/JavaVM.framework/Versions/A/Resources/en.lproj"
Copy the file named "DefaultApp.nib"
Go to "/System/Library/Frameworks/JavaVM.framework/Versions/A/Resources/German.lproj"
Paste "DefaultApp.nib"
Move the "Menu.strings" to another folder (for eg. create an "Java .lproj" in your document folder), so you can restore all changes if you want to
Start in recovery mode and open the terminal then, type "csrutil enable" to restore security settings
Thank to you Sr. Member for your solution that works fine (I don’t know how you find this solution)
For French language (or other language) do the same : but with French.Iproj directory instead of German.Iproj directory in step 6 (I think it will work the same with all languages if you select in step 6 your own language directory)... the Arduino menu will be back in your own language - in our case here in French
Shutdown your Mac
Start in recovery mode (Cmd + R when starting your mac) and open the terminal then, type "csrutil disable" (else you can't write in the /System folder)
Restart
Go to "/System/Library/Frameworks/JavaVM.framework/Versions/A/Resources/en.lproj"
Copy the file named "DefaultApp.nib"
Go to "/System/Library/Frameworks/JavaVM.framework/Versions/A/Resources/French.lproj"
Paste "DefaultApp.nib"
Move the "Menu.strings" to another folder (for eg. in your document folder, in case you want to restore later) and make sure you remove "Menu.strings" file from French.lproj directory (you will be asked to sign in your Admin password). If you come back later, after step 10, you will see that a new "Menu.strings" file has been created by the system in the French.lproj directory
Start in recovery mode and open the terminal then, type "csrutil enable" to restore security and restart your Mac
Merci Sr. Member, pour votre solution qui fonctionne bien (je ne sais pas comment vous trouvez cette solution).
Pour la langue française (ou autre langue) faire de même: mais avec le répertoire French.Iproj au lieu du répertoire German.Iproj à l'étape 6 (je pense que cela fonctionnera de la même manière avec toutes les langues si vous sélectionnez à l'étape 6 votre propre répertoire de langue) ... le menu Arduino sera de nouveau dans votre propre langue - dans notre cas ici en français
Arrêtez votre Mac
Commencez en mode Recovery (Cmd + R lorsque vous démarrez votre mac) et ouvrez le terminal, tapez "csrutil disable" (sinon vous ne pouvez pas écrire dans le dossier / System)
Redémarrez votre Mac
Accédez à "/ System / Library / Frameworks / JavaVM.framework / Versions / A / Resources / en.lproj "
Copiez le fichier nommé" DefaultApp.nib "
Accédez à" / System / Library/Frameworks/JavaVM.framework/Versions/A/Resources/French .lproj "
Collez" DefaultApp.nib "
Déplacez le fichier "Menu.strings "vers un autre dossier (par exemple, dans votre dossier de document, dans le cas où vous souhaiteriez restaurer plus tard) et assurez-vous d’avoir supprimé le fichier « Menu.strings " du répertoire french.lproj (vous devrez vous connecter à votre mot de passe Admin). Si vous revenez plus tard, après l'étape 10, vous verrez qu'un nouveau fichier "Menu.strings" a été créé par le système dans le répertoire French.lproj
Démarrez en mode de Recovery et ouvrez le terminal puis tapez "csrutil enable "pour restaurer la sécurité et redémarrez votre Mac