diff --git a/pkg/i18n/compose_test.go b/pkg/i18n/compose_test.go
index 0428bb21..0a95e9dd 100644
--- a/pkg/i18n/compose_test.go
+++ b/pkg/i18n/compose_test.go
@@ -248,6 +248,11 @@ func composeIntent(intent Intent, subject *Subject) *Composed {
 // can compose the same strings as the intent templates.
 // This turns the intents definitions into a comprehensive test suite.
 func TestGrammarComposition_MatchesIntents(t *testing.T) {
+	// Clear locale env vars to ensure British English fallback (en-GB)
+	t.Setenv("LANG", "")
+	t.Setenv("LC_ALL", "")
+	t.Setenv("LC_MESSAGES", "")
+
 	// Test subjects for validation
 	subjects := []struct {
 		noun  string
@@ -428,6 +433,11 @@ func TestProgress_AllIntentVerbs(t *testing.T) {
 
 // TestPastTense_AllIntentVerbs ensures PastTense works for all intent verbs.
 func TestPastTense_AllIntentVerbs(t *testing.T) {
+	// Clear locale env vars to ensure British English fallback (en-GB)
+	t.Setenv("LANG", "")
+	t.Setenv("LC_ALL", "")
+	t.Setenv("LC_MESSAGES", "")
+
 	expected := map[string]string{
 		// Destructive
 		"delete":    "deleted",
@@ -499,6 +509,11 @@ func TestPastTense_AllIntentVerbs(t *testing.T) {
 
 // TestGerund_AllIntentVerbs ensures Gerund works for all intent verbs.
 func TestGerund_AllIntentVerbs(t *testing.T) {
+	// Clear locale env vars to ensure British English fallback (en-GB)
+	t.Setenv("LANG", "")
+	t.Setenv("LC_ALL", "")
+	t.Setenv("LC_MESSAGES", "")
+
 	expected := map[string]string{
 		// Destructive
 		"delete":    "deleting",
diff --git a/pkg/i18n/i18n_test.go b/pkg/i18n/i18n_test.go
index a02bbac7..920bbd9b 100644
--- a/pkg/i18n/i18n_test.go
+++ b/pkg/i18n/i18n_test.go
@@ -44,10 +44,15 @@ func TestTranslateWithArgs(t *testing.T) {
 }
 
 func TestSetLanguage(t *testing.T) {
+	// Clear locale env vars to ensure fallback to en-GB
+	t.Setenv("LANG", "")
+	t.Setenv("LC_ALL", "")
+	t.Setenv("LC_MESSAGES", "")
+
 	svc, err := New()
 	require.NoError(t, err)
 
-	// Default is en-GB
+	// Default is en-GB (when no system locale detected)
 	assert.Equal(t, "en-GB", svc.Language())
 
 	// Setting invalid language should error
diff --git a/pkg/i18n/types.go b/pkg/i18n/types.go
index ac17aaaa..a84db9bd 100644
--- a/pkg/i18n/types.go
+++ b/pkg/i18n/types.go
@@ -408,6 +408,16 @@ var irregularVerbs = map[string]VerbForms{
 	"cancel": {Past: "cancelled", Gerund: "cancelling"}, "travel": {Past: "travelled", Gerund: "travelling"},
 	"label": {Past: "labelled", Gerund: "labelling"}, "model": {Past: "modelled", Gerund: "modelling"},
 	"level": {Past: "levelled", Gerund: "levelling"},
+	// British English spellings
+	"format":      {Past: "formatted", Gerund: "formatting"},
+	"analyse":     {Past: "analysed", Gerund: "analysing"},
+	"organise":    {Past: "organised", Gerund: "organising"},
+	"recognise":   {Past: "recognised", Gerund: "recognising"},
+	"realise":     {Past: "realised", Gerund: "realising"},
+	"customise":   {Past: "customised", Gerund: "customising"},
+	"optimise":    {Past: "optimised", Gerund: "optimising"},
+	"initialise":  {Past: "initialised", Gerund: "initialising"},
+	"synchronise": {Past: "synchronised", Gerund: "synchronising"},
 }
 
 // noDoubleConsonant contains multi-syllable verbs that don't double the final consonant.