diff --git a/advotracker_client/src/main.rs b/advotracker_client/src/main.rs
index e24af8e..5589902 100644
--- a/advotracker_client/src/main.rs
+++ b/advotracker_client/src/main.rs
@@ -57,26 +57,31 @@ static ADVOTRACKER_DE_DE: &str = include_str!("../assets/advotracker/advotracker
 fn get_lang() -> String {
     // get system environment
     let mut lang_id = env::var("LANG").unwrap_or_else(|_| "En".to_string());
-    lang_id = lang_id.substring(0,1).to_uppercase();  // "de" -> "De"
-    lang_id = lang_id.substring(0,2).to_string();     // "de_DE.UTF-8" -> "de"
-    info!("GUI-Language: preset to {:?}", lang_id);
+    let lang_variant = "";
 
-    // testing environment: read from .env file
+    // prepare lang_id to represent twine language prefix
+    // env: "de_DE.UTF-8" -> "De"
+    lang_id = lang_id.substring(0,2).to_string();
+    lang_id.replace_range(..1, &lang_id.substring(0,1).to_string().to_uppercase() );
+
+    // handle testing environment variables (.env file) with precedence
     dotenv().ok();
     match envy::from_env::<Environment>() {
         Ok(environment) => {
             if environment.test_lang != lang_id {
+                info!("GUI-Language: preset from .env to {:?}", lang_id);
                 lang_id = environment.test_lang;
-                lang_id = lang_id.substring(0,2).to_string();     // "de_DE.UTF-8" -> "de"
-                lang_id = lang_id.substring(0,1).to_uppercase();  // "de" -> "De"
+                lang_id = lang_id.substring(0,2).to_string();
+                lang_id.replace_range(..1, &lang_id.substring(0,1).to_string().to_uppercase() );
             }
         },
         Err(e) => { info!(target: "advotracker", "{}", e) }
     }
-    trace!(target: "advotracker", lang_id = ?lang_id);
+
+    let lang = format!("Lang::{}(\"{}\")", lang_id, lang_variant);
+    trace!(target: "advotracker", lang_id = ?lang_id, lang = ?lang);
 
     // return the active language
-    let lang = format!("Lang::{}(\"\")", lang_id);
     lang
 }
 
@@ -92,7 +97,7 @@ cfg_if! {
             ))
         }
         fn theme_fluent() -> Theme {
-            orbtk::widgets::themes::theme_orbtk::register_fluent_fonts(Theme::from_config(
+            orbtk::widgets::themes::theme_fluent::register_fluent_fonts(Theme::from_config(
                 ThemeConfig::from(FLUENT_DARK_EXT)
                     .extend(ThemeConfig::from(THEME_FLUENT))
                     .extend(ThemeConfig::from(THEME_FLUENT_COLORS_DARK))
@@ -146,8 +151,10 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
 
     tracing::subscriber::with_default(collector, || {
         // get system environment
-        let _my_lang = get_lang();
+        let get_lang = get_lang();
+        println!("get_lang returns: {:?}", get_lang);
         let lang = Lang::De("");
+        println!("lang returns: {:?}", lang);
 
         let mut state = t!(state_started => lang);
         let mut res = t!(parse_environment => lang);
@@ -185,11 +192,12 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         // use this only if you want to run it as web application.
         orbtk::initialize();
 
-        // Preset localization and language from given environment.
-        // if no dictionary is set for the chosen default language
-        // the content of the text property will be drawn.
+        // Preset localization and language to "de_DE".
+        // If the choosen language is not associated with a corresponding
+        // dictionary, the contents of the default text property will be
+        // rendered.
         let localization = RonLocalization::create()
-            .language("de")
+            .language("de_DE")
             .dictionary("de_DE", ADVOTRACKER_DE_DE)
             .build();