[feature] Set/show instance language(s); show post language on frontend (#2362)

* update go text, include text/display

* [feature] Set instance langs, show post lang on frontend

* go fmt

* WebGet

* set language for whole article, don't use FA icon

* mention instance languages + other optional config vars

* little tweak

* put languages in config properly

* warn log language parse

* change some naming around

* tidy up validate a bit

* lint

* rename LanguageTmpl in template

2 files changed, 25 insertions, 0 deletions

diff --git a/docs/getting_started/installation/container.md b/docs/getting_started/installation/container.md
index 25e634607..c14e0a999 100644
--- a/docs/getting_started/installation/container.md
+++ b/docs/getting_started/installation/container.md
@@ -76,6 +76,21 @@ If you want to use [LetsEncrypt](../../configuration/tls.md) for TLS certificate
 2. Remove the `#` before `- "80:80"` in the `ports` section.
 3. (Optional) Set `GTS_LETSENCRYPT_EMAIL_ADDRESS` to a valid email address to receive certificate expiry warnings etc.
 
+!!! info "Optional configuration"
+    
+    There are many other configuration options documented in the config.yaml file, which you can use to further customize the behavior of your GoToSocial instance. These use sensible defaults where possible, so you don't necessarily need to make any changes to them right now, but here are a few you may be interested in:
+    
+    - `GTS_INSTANCE_LANGUAGES`: array of [BCP47 language tags](https://en.wikipedia.org/wiki/IETF_language_tag) which determines the preferred languages of your instance.
+    - `GTS_MEDIA_REMOTE_CACHE_DAYS`: number of days to keep remote media cached in storage.
+    - `GTS_SMTP_*`: settings to allow your GoToSocial instance to connect to an email server and send notification emails.
+
+    If you decide to set/change any of these variables later on, be sure to restart your GoToSocial instance after making the changes.
+    
+
+!!! tip
+    
+    For help translating variable names from the config.yaml file to environment variables, refer to the [configuration section](../../configuration/index.md#environment-variables).
+
 ## Start GoToSocial
 
 With those small changes out of the way, you can now start GoToSocial with the following command:
diff --git a/docs/getting_started/installation/metal.md b/docs/getting_started/installation/metal.md
index bac4c2f26..facc13326 100644
--- a/docs/getting_started/installation/metal.md
+++ b/docs/getting_started/installation/metal.md
@@ -61,6 +61,16 @@ Now open the file in your text editor of choice so that you can set some importa
 
 The above options assume you're using SQLite as your database. If you want to use Postgres instead, see [here](../../configuration/database.md) for the config options.
 
+!!! info "Optional configuration"
+    
+    There are many other configuration options documented in the config.yaml file, which you can use to further customize the behavior of your GoToSocial instance. These use sensible defaults where possible, so you don't necessarily need to make any changes to them right now, but here are a few you may be interested in:
+    
+    - `instance-languages`: array of [BCP47 language tags](https://en.wikipedia.org/wiki/IETF_language_tag) which determines the preferred languages of your instance.
+    - `media-remote-cache-days`: number of days to keep remote media cached in storage.
+    - `smtp-*`: settings to allow your GoToSocial instance to connect to an email server and send notification emails.
+
+    If you decide to set/change any of these variables later on, be sure to restart your GoToSocial instance after making the changes.
+
 ## Run the Binary
 
 You can now run the binary.