diff --git a/internal/base/validator/validator.go b/internal/base/validator/validator.go
index 9c7f6ec41..2b7374b19 100644
--- a/internal/base/validator/validator.go
+++ b/internal/base/validator/validator.go
@@ -24,6 +24,7 @@ import (
 	"fmt"
 	"reflect"
 	"strings"
+	"sync"
 	"unicode"
 
 	"github.com/apache/answer/internal/base/reason"
@@ -96,7 +97,10 @@ type FormErrorField struct {
 }
 
 // GlobalValidatorMapping is a mapping from validator to translator used
-var GlobalValidatorMapping = make(map[i18n.Language]*MyValidator, 0)
+var (
+	GlobalValidatorMapping = make(map[i18n.Language]*MyValidator, 0)
+	validatorMappingMu     sync.RWMutex
+)
 
 func init() {
 	for _, t := range allLanguageTranslators {
@@ -180,9 +184,44 @@ func createDefaultValidator(la i18n.Language) *validator.Validate {
 }
 
 func GetValidatorByLang(lang i18n.Language) *MyValidator {
-	if GlobalValidatorMapping[lang] != nil {
-		return GlobalValidatorMapping[lang]
+	validatorMappingMu.RLock()
+	if v := GlobalValidatorMapping[lang]; v != nil {
+		validatorMappingMu.RUnlock()
+		return v
+	}
+	validatorMappingMu.RUnlock()
+
+	baseLang := string(lang)
+	if idx := strings.IndexAny(baseLang, "_-"); idx > 0 {
+		baseLang = baseLang[:idx]
 	}
+
+	for _, t := range allLanguageTranslators {
+		tBase := string(t.La)
+		if idx := strings.IndexAny(tBase, "_-"); idx > 0 {
+			tBase = tBase[:idx]
+		}
+		if strings.EqualFold(baseLang, tBase) {
+			validatorMappingMu.Lock()
+			defer validatorMappingMu.Unlock()
+			if v := GlobalValidatorMapping[lang]; v != nil {
+				return v
+			}
+			tran, val := getTran(t.Lo), createDefaultValidator(lang)
+			if t.RegisterFunc != nil {
+				if err := t.RegisterFunc(val, tran); err != nil {
+					log.Error(err)
+					break
+				}
+			}
+			v := &MyValidator{Validate: val, Tran: tran, Lang: lang}
+			GlobalValidatorMapping[lang] = v
+			return v
+		}
+	}
+
+	validatorMappingMu.RLock()
+	defer validatorMappingMu.RUnlock()
 	return GlobalValidatorMapping[i18n.DefaultLanguage]
 }
 
@@ -196,12 +235,16 @@ func (m *MyValidator) Check(value any) (errFields []*FormErrorField, err error)
 			if len(field.ErrorField) == 0 {
 				continue
 			}
-			firstRune := []rune(field.ErrorMsg)[0]
+			runes := []rune(field.ErrorMsg)
+			if len(runes) == 0 {
+				continue
+			}
+			firstRune := runes[0]
 			if !unicode.IsLetter(firstRune) || !unicode.Is(unicode.Latin, firstRune) {
 				continue
 			}
 			upperFirstRune := unicode.ToUpper(firstRune)
-			field.ErrorMsg = string(upperFirstRune) + field.ErrorMsg[1:]
+			field.ErrorMsg = string(upperFirstRune) + string(runes[1:])
 			if !strings.HasSuffix(field.ErrorMsg, ".") {
 				field.ErrorMsg += "."
 			}
diff --git a/internal/base/validator/validator_test.go b/internal/base/validator/validator_test.go
new file mode 100644
index 000000000..583e2bf2e
--- /dev/null
+++ b/internal/base/validator/validator_test.go
@@ -0,0 +1,73 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package validator
+
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"github.com/segmentfault/pacman/i18n"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type sampleCommentReq struct {
+	OriginalText string `validate:"required,notblank,gte=2,lte=5" json:"original_text"`
+}
+
+type sampleAccentedFieldReq struct {
+	Email string `validate:"required,email" json:"émail"`
+}
+
+func TestGetValidatorByLang_RegionalLocaleFallback(t *testing.T) {
+	req := &sampleCommentReq{OriginalText: "123456"}
+
+	esMXValidator := GetValidatorByLang(i18n.Language("es_MX"))
+	require.NotNil(t, esMXValidator)
+	assert.Equal(t, i18n.Language("es_MX"), esMXValidator.Lang)
+
+	errFields, err := esMXValidator.Check(req)
+	require.Error(t, err)
+	require.Len(t, errFields, 1)
+	assert.Contains(t, errFields[0].ErrorMsg, "debe tener un máximo de 5")
+
+	ptBRValidator := GetValidatorByLang(i18n.Language("pt_BR"))
+	require.NotNil(t, ptBRValidator)
+	assert.Equal(t, i18n.Language("pt_BR"), ptBRValidator.Lang)
+
+	errFieldsPT, errPT := ptBRValidator.Check(req)
+	require.Error(t, errPT)
+	require.Len(t, errFieldsPT, 1)
+	assert.Contains(t, errFieldsPT[0].ErrorMsg, "máximo")
+}
+
+func TestCheck_MultiByteLatinCapitalization(t *testing.T) {
+	req := &sampleAccentedFieldReq{Email: "not-an-email"}
+
+	esValidator := GetValidatorByLang(i18n.LanguageSpanish)
+	errFields, err := esValidator.Check(req)
+	require.Error(t, err)
+	require.Len(t, errFields, 1)
+
+	msg := errFields[0].ErrorMsg
+	assert.True(t, utf8.ValidString(msg), "error message must be valid UTF-8, got: %q", msg)
+	assert.True(t, strings.HasPrefix(msg, "Émail "), "expected prefix 'Émail ', got: %q", msg)
+}