Fix SAML login "something went wrong" when language list = 1 (#5750)

# Description of Changes

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- What was changed
- Why the change was made
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Closes #(issue_number)
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## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

testing/compose/docker-compose-keycloak-saml.yml

@@ -74,7 +74,7 @@ services:
       DOCKER_ENABLE_SECURITY: "true"
       SECURITY_ENABLELOGIN: "true"
       SECURITY_LOGINMETHOD: "${SECURITY_LOGINMETHOD:-all}"
-      SYSTEM_DEFAULTLOCALE: en-US
+      SYSTEM_DEFAULTLOCALE: "${SYSTEM_DEFAULTLOCALE:-en-US}"
       SYSTEM_BACKENDURL: "http://localhost:8080"
 
       # Enterprise License (required for SAML)

testing/compose/start-saml-test.sh

@@ -13,24 +13,48 @@ echo -e "${BLUE}╚════════════════════
 echo ""
 
 AUTO_LOGIN=false
+DEFAULT_LANGUAGE="en-US"
 COMPOSE_UP_ARGS=(-d --build)
-for arg in "$@"; do
-    case "$arg" in
+while [[ $# -gt 0 ]]; do
+    case "$1" in
         --auto)
             AUTO_LOGIN=true
+            shift
             ;;
         --nobuild)
             COMPOSE_UP_ARGS=(-d)
+            shift
+            ;;
+        --language)
+            if [[ -z "${2:-}" ]]; then
+                echo -e "${RED}Missing value for --language${NC}"
+                exit 1
+            fi
+            DEFAULT_LANGUAGE="$2"
+            shift 2
+            ;;
+        --language=*)
+            DEFAULT_LANGUAGE="${1#*=}"
+            shift
+            ;;
+        -l)
+            if [[ -z "${2:-}" ]]; then
+                echo -e "${RED}Missing value for -l${NC}"
+                exit 1
+            fi
+            DEFAULT_LANGUAGE="$2"
+            shift 2
             ;;
         -h|--help)
-            echo "Usage: $0 [--auto] [--nobuild]"
+            echo "Usage: $0 [--auto] [--nobuild] [--language <locale>]"
             echo ""
             echo "  --auto     Enable SSO auto-login and force SAML-only login method"
             echo "  --nobuild  Skip building images (use existing images)"
+            echo "  --language Set system default locale (e.g. de-DE, sv-SE)"
             exit 0
             ;;
         *)
-            echo -e "${RED}Unknown option: $arg${NC}"
+            echo -e "${RED}Unknown option: $1${NC}"
             exit 1
             ;;
     esac
@@ -65,6 +89,10 @@ if [ "$AUTO_LOGIN" = true ]; then
     echo ""
 fi
 
+export SYSTEM_DEFAULTLOCALE="$DEFAULT_LANGUAGE"
+echo -e "${GREEN}✓ Default locale set to: ${SYSTEM_DEFAULTLOCALE}${NC}"
+echo ""
+
 echo -e "${YELLOW}▶ Starting Keycloak (SAML) containers...${NC}"
 docker-compose -f docker-compose-keycloak-saml.yml up "${COMPOSE_UP_ARGS[@]}" keycloak-saml-db keycloak-saml