6 files changed, 49 insertions, 23 deletions
diff --git a/server/ui/form/auth.go b/server/ui/form/auth.go
index 3cfc217..6849339 100644
--- a/server/ui/form/auth.go
+++ b/server/ui/form/auth.go
@@ -5,23 +5,27 @@
 package form
 
 import (
-	"errors"
 	"net/http"
+
+	"github.com/miniflux/miniflux2/errors"
 )
 
+// AuthForm represents the authentication form.
 type AuthForm struct {
 	Username string
 	Password string
 }
 
+// Validate makes sure the form values are valid.
 func (a AuthForm) Validate() error {
 	if a.Username == "" || a.Password == "" {
-		return errors.New("All fields are mandatory.")
+		return errors.NewLocalizedError("All fields are mandatory.")
 	}
 
 	return nil
 }
 
+// NewAuthForm returns a new AuthForm.
 func NewAuthForm(r *http.Request) *AuthForm {
 	return &AuthForm{
 		Username: r.FormValue("username"),
diff --git a/server/ui/form/category.go b/server/ui/form/category.go
index 510d1b4..f977b7a 100644
--- a/server/ui/form/category.go
+++ b/server/ui/form/category.go
@@ -5,9 +5,10 @@
 package form
 
 import (
-	"errors"
-	"github.com/miniflux/miniflux2/model"
 	"net/http"
+
+	"github.com/miniflux/miniflux2/errors"
+	"github.com/miniflux/miniflux2/model"
 )
 
 // CategoryForm represents a feed form in the UI
@@ -15,18 +16,21 @@ type CategoryForm struct {
 	Title string
 }
 
+// Validate makes sure the form values are valid.
 func (c CategoryForm) Validate() error {
 	if c.Title == "" {
-		return errors.New("The title is mandatory.")
+		return errors.NewLocalizedError("The title is mandatory.")
 	}
 	return nil
 }
 
+// Merge update the given category fields.
 func (c CategoryForm) Merge(category *model.Category) *model.Category {
 	category.Title = c.Title
 	return category
 }
 
+// NewCategoryForm returns a new CategoryForm.
 func NewCategoryForm(r *http.Request) *CategoryForm {
 	return &CategoryForm{
 		Title: r.FormValue("title"),
diff --git a/server/ui/form/feed.go b/server/ui/form/feed.go
index e21e6ca..8a8cf20 100644
--- a/server/ui/form/feed.go
+++ b/server/ui/form/feed.go
@@ -5,10 +5,11 @@
 package form
 
 import (
-	"errors"
-	"github.com/miniflux/miniflux2/model"
 	"net/http"
 	"strconv"
+
+	"github.com/miniflux/miniflux2/errors"
+	"github.com/miniflux/miniflux2/model"
 )
 
 // FeedForm represents a feed form in the UI
@@ -22,11 +23,12 @@ type FeedForm struct {
 // ValidateModification validates FeedForm fields
 func (f FeedForm) ValidateModification() error {
 	if f.FeedURL == "" || f.SiteURL == "" || f.Title == "" || f.CategoryID == 0 {
-		return errors.New("All fields are mandatory.")
+		return errors.NewLocalizedError("All fields are mandatory.")
 	}
 	return nil
 }
 
+// Merge updates the fields of the given feed.
 func (f FeedForm) Merge(feed *model.Feed) *model.Feed {
 	feed.Category.ID = f.CategoryID
 	feed.Title = f.Title
diff --git a/server/ui/form/settings.go b/server/ui/form/settings.go
index 1e40b97..3d37a0f 100644
--- a/server/ui/form/settings.go
+++ b/server/ui/form/settings.go
@@ -5,11 +5,13 @@
 package form
 
 import (
-	"errors"
-	"github.com/miniflux/miniflux2/model"
 	"net/http"
+
+	"github.com/miniflux/miniflux2/errors"
+	"github.com/miniflux/miniflux2/model"
 )
 
+// SettingsForm represents the settings form.
 type SettingsForm struct {
 	Username     string
 	Password     string
@@ -19,6 +21,7 @@ type SettingsForm struct {
 	Timezone     string
 }
 
+// Merge updates the fields of the given user.
 func (s *SettingsForm) Merge(user *model.User) *model.User {
 	user.Username = s.Username
 	user.Theme = s.Theme
@@ -32,24 +35,26 @@ func (s *SettingsForm) Merge(user *model.User) *model.User {
 	return user
 }
 
+// Validate makes sure the form values are valid.
 func (s *SettingsForm) Validate() error {
 	if s.Username == "" || s.Theme == "" || s.Language == "" || s.Timezone == "" {
-		return errors.New("The username, theme, language and timezone fields are mandatory.")
+		return errors.NewLocalizedError("The username, theme, language and timezone fields are mandatory.")
 	}
 
 	if s.Password != "" {
 		if s.Password != s.Confirmation {
-			return errors.New("Passwords are not the same.")
+			return errors.NewLocalizedError("Passwords are not the same.")
 		}
 
 		if len(s.Password) < 6 {
-			return errors.New("You must use at least 6 characters")
+			return errors.NewLocalizedError("You must use at least 6 characters")
 		}
 	}
 
 	return nil
 }
 
+// NewSettingsForm returns a new SettingsForm.
 func NewSettingsForm(r *http.Request) *SettingsForm {
 	return &SettingsForm{
 		Username:     r.FormValue("username"),
diff --git a/server/ui/form/subscription.go b/server/ui/form/subscription.go
index 6696b22..ca1c605 100644
--- a/server/ui/form/subscription.go
+++ b/server/ui/form/subscription.go
@@ -5,24 +5,28 @@
 package form
 
 import (
-	"errors"
 	"net/http"
 	"strconv"
+
+	"github.com/miniflux/miniflux2/errors"
 )
 
+// SubscriptionForm represents the subscription form.
 type SubscriptionForm struct {
 	URL        string
 	CategoryID int64
 }
 
+// Validate makes sure the form values are valid.
 func (s *SubscriptionForm) Validate() error {
 	if s.URL == "" || s.CategoryID == 0 {
-		return errors.New("The URL and the category are mandatory.")
+		return errors.NewLocalizedError("The URL and the category are mandatory.")
 	}
 
 	return nil
 }
 
+// NewSubscriptionForm returns a new SubscriptionForm.
 func NewSubscriptionForm(r *http.Request) *SubscriptionForm {
 	categoryID, err := strconv.Atoi(r.FormValue("category_id"))
 	if err != nil {
diff --git a/server/ui/form/user.go b/server/ui/form/user.go
index 1197b48..5319cb8 100644
--- a/server/ui/form/user.go
+++ b/server/ui/form/user.go
@@ -5,11 +5,13 @@
 package form
 
 import (
-	"errors"
-	"github.com/miniflux/miniflux2/model"
 	"net/http"
+
+	"github.com/miniflux/miniflux2/errors"
+	"github.com/miniflux/miniflux2/model"
 )
 
+// UserForm represents the user form.
 type UserForm struct {
 	Username     string
 	Password     string
@@ -17,40 +19,43 @@ type UserForm struct {
 	IsAdmin      bool
 }
 
+// ValidateCreation validates user creation.
 func (u UserForm) ValidateCreation() error {
 	if u.Username == "" || u.Password == "" || u.Confirmation == "" {
-		return errors.New("All fields are mandatory.")
+		return errors.NewLocalizedError("All fields are mandatory.")
 	}
 
 	if u.Password != u.Confirmation {
-		return errors.New("Passwords are not the same.")
+		return errors.NewLocalizedError("Passwords are not the same.")
 	}
 
 	if len(u.Password) < 6 {
-		return errors.New("You must use at least 6 characters.")
+		return errors.NewLocalizedError("You must use at least 6 characters.")
 	}
 
 	return nil
 }
 
+// ValidateModification validates user modification.
 func (u UserForm) ValidateModification() error {
 	if u.Username == "" {
-		return errors.New("The username is mandatory.")
+		return errors.NewLocalizedError("The username is mandatory.")
 	}
 
 	if u.Password != "" {
 		if u.Password != u.Confirmation {
-			return errors.New("Passwords are not the same.")
+			return errors.NewLocalizedError("Passwords are not the same.")
 		}
 
 		if len(u.Password) < 6 {
-			return errors.New("You must use at least 6 characters.")
+			return errors.NewLocalizedError("You must use at least 6 characters.")
 		}
 	}
 
 	return nil
 }
 
+// ToUser returns a User from the form values.
 func (u UserForm) ToUser() *model.User {
 	return &model.User{
 		Username: u.Username,
@@ -59,6 +64,7 @@ func (u UserForm) ToUser() *model.User {
 	}
 }
 
+// Merge updates the fields of the given user.
 func (u UserForm) Merge(user *model.User) *model.User {
 	user.Username = u.Username
 	user.IsAdmin = u.IsAdmin
@@ -70,6 +76,7 @@ func (u UserForm) Merge(user *model.User) *model.User {
 	return user
 }
 
+// NewUserForm returns a new UserForm.
 func NewUserForm(r *http.Request) *UserForm {
 	return &UserForm{
 		Username:     r.FormValue("username"),