diff --git a/CHANGELOG.md b/CHANGELOG.md
index bc174ea..7c6b1ca 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -28,6 +28,14 @@ to structure this file.
   - Smart log filtering that respects the configured log level
   - Debug messages are now filtered out by default, providing cleaner output
 
+### Fixed
+- LocalizationParser.ps1 now defaults to en-US culture when UICulture parameter is not provided
+  - Fixes Import-LocalizedData failures in environments with invariant culture
+  - Ensures localization files can be found in culture-specific subdirectories
+- Updated Pester configuration syntax in psake.ps1 for compatibility with Pester 5.x
+  - Replaced deprecated [PesterConfiguration]@{} with New-PesterConfiguration
+  - Fixed PassThru parameter usage for modern Pester API
+
 ## [0.1.0] Initial Release
 
 - Foundational script `LocalizationParser` looks for `psm1` that container
diff --git a/psake.ps1 b/psake.ps1
index ca76262..2077739 100644
--- a/psake.ps1
+++ b/psake.ps1
@@ -7,9 +7,10 @@ Properties {
   $script:outDir = 'out'
   $script:scriptDir = $PSScriptRoot
 
-  $script:PesterConfiguration = [PesterConfiguration]@{}
+  $script:PesterConfiguration = New-PesterConfiguration
   $script:PesterConfiguration.Output.CIFormat = 'Auto'
   $script:PesterConfiguration.Run.Path = ".\tests\"
+  $script:PesterConfiguration.Run.PassThru = $true
 }
 
 Task Default -Depends Test
@@ -77,7 +78,8 @@ Task VscodeTest -Depends InstallDependencies {
 Task Pester {
   Write-Host '🧪 Running Pester tests...'
   try {
-    $results = Invoke-Pester -Configuration $script:PesterConfiguration -PassThru
+    Import-Module Pester
+    $results = Invoke-Pester -Configuration $script:PesterConfiguration
     if ($results.FailedCount -gt 0) {
       Write-Error '❌ Pester tests failed. Please fix the issues before packaging.'
       exit 1
diff --git a/resources/LocalizationParser.ps1 b/resources/LocalizationParser.ps1
index 150a83f..ba0ccca 100644
--- a/resources/LocalizationParser.ps1
+++ b/resources/LocalizationParser.ps1
@@ -136,6 +136,9 @@ if (Test-Path $file) {
       }
       if ($null -ne $UICulture -and -not [String]::IsNullOrEmpty($UICulture.Name)) {
         $splat['UICulture'] = $UICulture.Name
+      } else {
+        # Default to en-US when no UICulture is specified
+        $splat['UICulture'] = 'en-US'
       }
       # Override the base directory if its set
       $splat['BaseDirectory'] = $parentDirectory