Ghyslain Drolet

Simple Login SC does just what it means
Simple Login SC does not mess with other plugins because it does just login or logout a user. Nothing more. Nothing less. 
It uses the core functions of WordPress thus not slowing down your site. No fancy stuff or hard settings. This is just a login plugin!
Using Simple Login SC is absolutely easy
Just type the shortcode where you want a login form to show. 
Use [sl_shortcode] shortcode to add a login form to a page, post or in a text/html widget. 
You can optionally set the labels for “username”, “password”, the submit button and/or the welcome message, the logout text. Just by adding text to the shortcode.
Usage
Example: [sl_shortcode username_label=”What is your name?” password_label=”Password Please!” button_text=”Let me in!” welcome_text=”Hello” logouttext=”Let’s go outside!”]
This is very useful if the language pack is not available in your language or if you have a multilangual site running WPML. 
If you do not set one or all of the optional text, the default text of WordPress and the plugin will be used.

Simple Login SC

Adds a simple login form via a shortcode and does not add any extraneous code to slow your website. It just uses the core functions of WordPress.

ThemeCatcher

With this add-on, a form can be translated into multiple languages using WPML. Gone are the days of having duplicate forms for each language!
<h3>Features</h3>
Translate unlimited forms into other languages through WPML.
Deep integration
All user-facing strings are fully translatable, including all form settings, fields settings and validation error messages. Emails sent to users can also be translated, along with the confirmation (success) message shown after the form is submitted.
Advanced WPML compatibility
Compatible with both the String Translation workflow, and the Advanced Translation Editor.
Datepicker/timepicker support
Automatically converts the locale of the datepickers and timepickers into the current WPML language. The dates and times will be automatically formatted according to regional standards.
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Note: this plugin is a free add-on for the <a href="https://www.quform.com/" rel="nofollow ugc">Quform Premium WordPress Form Builder plugin</a>. For this plugin to function, Quform version 2.16.0 or later, WPML version 3.2 or later, and the WPML String Translation plugin must be installed.
</blockquote>

Quform WPML

Translate Quform forms into multiple languages using WPML.

Simple Login SC vs Quform WPML