diff --git a/changelog/unreleased/default-locale-activitylog.md b/changelog/unreleased/default-locale-activitylog.md
new file mode 100644
index 00000000000..695dec4ef0c
--- /dev/null
+++ b/changelog/unreleased/default-locale-activitylog.md
@@ -0,0 +1,5 @@
+Enhancement: Allow setting default locale of activitylog
+
+Allows setting the default locale via `OCIS_DEFAULT_LANGUAGE` envvar
+
+https://github.com/owncloud/ocis/pull/9892
diff --git a/services/activitylog/README.md b/services/activitylog/README.md
index b7238194a84..1b446f1b378 100644
--- a/services/activitylog/README.md
+++ b/services/activitylog/README.md
@@ -13,3 +13,29 @@ Log services like the `activitylog`, `userlog`, `clientlog` and `sse` are respon
 ## Activitylog Store
 
 The `activitylog` stores activities for each resource. It works in conjunction with the `eventhistory` service to keep the data it needs to store to a minimum.
+
+## Translations
+
+The `activitylog` service has embedded translations sourced via transifex to provide a basic set of translated languages. These embedded translations are available for all deployment scenarios. In addition, the service supports custom translations, though it is currently not possible to just add custom translations to embedded ones. If custom translations are configured, the embedded ones are not used. To configure custom translations, the `ACTIVITYLOG_TRANSLATION_PATH` environment variable needs to point to a base folder that will contain the translation files. This path must be available from all instances of the activitylog service, a shared storage is recommended. Translation files must be of type  [.po](https://www.gnu.org/software/gettext/manual/html_node/PO-Files.html#PO-Files) or [.mo](https://www.gnu.org/software/gettext/manual/html_node/Binaries.html). For each language, the filename needs to be `activitylog.po` (or `activitylog.mo`) and stored in a folder structure defining the language code. In general the path/name pattern for a translation file needs to be:
+
+```text
+{ACTIVITYLOG_TRANSLATION_PATH}/{language-code}/LC_MESSAGES/activitylog.po
+```
+
+The language code pattern is composed of `language[_territory]` where  `language` is the base language and `_territory` is optional and defines a country.
+
+For example, for the language `de`, one needs to place the corresponding translation files to `{ACTIVITYLOG_TRANSLATION_PATH}/de_DE/LC_MESSAGES/activitylog.po`.
+
+<!-- also see the notifications readme -->
+
+Important: For the time being, the embedded ownCloud Web frontend only supports the main language code but does not handle any territory. When strings are available in the language code `language_territory`, the web frontend does not see it as it only requests `language`. In consequence, any translations made must exist in the requested `language` to avoid a fallback to the default.
+
+### Translation Rules
+
+*   If a requested language code is not available, the service tries to fall back to the base language if available. For example, if the requested language-code `de_DE` is not available, the service tries to fall back to translations in the `de` folder.
+*   If the base language `de` is also not available, the service falls back to the system's default English (`en`),
+which is the source of the texts provided by the code.
+
+## Default Language
+
+The default language can be defined via the `OCIS_DEFAULT_LANGUAGE` environment variable. See the `settings` service for a detailed description.
diff --git a/services/activitylog/pkg/config/config.go b/services/activitylog/pkg/config/config.go
index 7c84b13178d..d4472f0884e 100644
--- a/services/activitylog/pkg/config/config.go
+++ b/services/activitylog/pkg/config/config.go
@@ -26,6 +26,9 @@ type Config struct {
 	HTTP         HTTP          `yaml:"http"`
 	TokenManager *TokenManager `yaml:"token_manager"`
 
+	TranslationPath string `yaml:"translation_path" env:"OCIS_TRANSLATION_PATH;ACTIVITYLOG_TRANSLATION_PATH" desc:"(optional) Set this to a path with custom translations to overwrite the builtin translations. Note that file and folder naming rules apply, see the documentation for more details." introductionVersion:"%%NEXT%%"`
+	DefaultLanguage string `yaml:"default_language" env:"OCIS_DEFAULT_LANGUAGE" desc:"The default language used by services and the WebUI. If not defined, English will be used as default. See the documentation for more details." introductionVersion:"%%NEXT%%"`
+
 	ServiceAccount ServiceAccount `yaml:"service_account"`
 
 	Context context.Context `yaml:"-"`
diff --git a/services/activitylog/pkg/config/defaults/defaultconfig.go b/services/activitylog/pkg/config/defaults/defaultconfig.go
index 00103af6be1..0f434e5baf6 100644
--- a/services/activitylog/pkg/config/defaults/defaultconfig.go
+++ b/services/activitylog/pkg/config/defaults/defaultconfig.go
@@ -37,7 +37,8 @@ func DefaultConfig() *config.Config {
 			Database: "activitylog",
 			Table:    "",
 		},
-		RevaGateway: shared.DefaultRevaConfig().Address,
+		RevaGateway:     shared.DefaultRevaConfig().Address,
+		DefaultLanguage: "en",
 		HTTP: config.HTTP{
 			Addr:      "127.0.0.1:0",
 			Root:      "/",
diff --git a/services/activitylog/pkg/service/http.go b/services/activitylog/pkg/service/http.go
index d47e2e71811..4c2f54064d0 100644
--- a/services/activitylog/pkg/service/http.go
+++ b/services/activitylog/pkg/service/http.go
@@ -164,9 +164,8 @@ func (s *ActivitylogService) HandleGetItemActivities(w http.ResponseWriter, r *h
 			continue
 		}
 
-		// FIXME: configurable default locale?
 		loc := l10n.MustGetUserLocale(r.Context(), activeUser.GetId().GetOpaqueId(), r.Header.Get(l10n.HeaderAcceptLanguage), s.valService)
-		t := l10n.NewTranslatorFromCommonConfig("en", _domain, "", _localeFS, _localeSubPath)
+		t := l10n.NewTranslatorFromCommonConfig(s.cfg.DefaultLanguage, _domain, s.cfg.TranslationPath, _localeFS, _localeSubPath)
 
 		resp.Activities = append(resp.Activities, NewActivity(t.Translate(message, loc), ts, e.GetId(), vars))
 	}