TimeZones

The timezones shown in the app are controlled by the LSTimeZones string-array user default (UserDefaults).

There is a legacy in libFoundation based OGo that "CET"(/"CEST") is called "MET"(/"MST").

GNUstep Base

In the Ubuntu GNUstep build the timezone definitions are located in:

/usr/share/GNUstep/Libraries/gnustep-base/Versions/1.29/Resources/NSTimeZones

GNUstep_zones
abbreviations
abbreviations.plist
localtime
nstimezone.m
preferred_abbreviations.plist
regions
zones

localtime:

Etc/UTC

zones/

Africa      Chile    GB-Eire    Israel     Navajo     US                 right
America     Cuba     GMT        Jamaica    PRC        UTC                tzdata.zi
Antarctica  EET      GMT+0      Japan      PST8PDT    Universal          zone.tab
Arctic      EST      GMT-0      Kwajalein  Pacific    W-SU               zone1970.tab
Asia        EST5EDT  GMT0       Libya      Poland     WET                zonenow.tab
Atlantic    Egypt    Greenwich  MET        Portugal   Zulu
Australia   Eire     HST        MST        ROC        iso3166.tab
Brazil      Etc      Hongkong   MST7MDT    ROK        leap-seconds.list
CET         Europe   Iceland    Mexico     Singapore  leapseconds
CST6CDT     Factory  Indian     NZ         Turkey     localtime
Canada      GB       Iran       NZ-CHAT    UCT        posixrules

zones/Europe

Amsterdam   Budapest     Jersey       Malta      Riga        Tallinn    Warsaw
Andorra     Busingen     Kaliningrad  Mariehamn  Rome        Tirane     Zagreb
Astrakhan   Chisinau     Kiev         Minsk      Samara      Tiraspol   Zaporozhye
Athens      Copenhagen   Kirov        Monaco     San_Marino  Ulyanovsk  Zurich
Belfast     Dublin       Kyiv         Moscow     Sarajevo    Uzhgorod
Belgrade    Gibraltar    Lisbon       Nicosia    Saratov     Vaduz
Berlin      Guernsey     Ljubljana    Oslo       Simferopol  Vatican
Bratislava  Helsinki     London       Paris      Skopje      Vienna
Brussels    Isle_of_Man  Luxembourg   Podgorica  Sofia       Vilnius
Bucharest   Istanbul     Madrid       Prague     Stockholm   Volgograd

zones/Europe/Berlin (binary tzdata file)

zones/Europe/Berlin: timezone data (fat), version 2, 9 gmt time flags, 9 std time flags, no leap seconds, 143 transition times, 9 local time types, 18 abbreviation chars

abbreviations.plist

{
    ADT = "America/Halifax";
    AFT = "Asia/Kabul";
    AKDT = "America/Juneau";
...
    CEST = "Europe/Paris";
    CET = "Europe/Paris";
...
    GMT = GMT;
...
    UTC = UTC;
...
}

abbreviations (prefix may have dupes)

+05     Antarctica/Mawson
-00     Antarctica/Mawson
+06     Antarctica/Mawson
AEDT    Antarctica/Macquarie
-00     Antarctica/Macquarie
AEST    Antarctica/Macquarie
...
CEST    Africa/Ceuta
WEST    Africa/Ceuta
CET     Africa/Ceuta
...
CET     Africa/Tripoli
...

regions

0 Antarctica/Mawson
0 Antarctica/Macquarie
...
18 US/East-Indiana
0 Greenwich
23 Eire
...
0 Africa/Sao_Tome
22 GMT-2
8 GMT+8
1 GMT+1
...
0 Zulu
0 GMT0
18 CST6CDT
23 GB
0 root/etc/localtime
0 Etc/Greenwich
...
1 Europe/Budapest
0 Europe/Berlin
0 Europe/Brussels