Custom multilingual inputs - opencart - input

Question

What is the pattern for creating a multilingual input in opencart for admin side.
For example I want to have two List Description Limit inputs, one for each language.
Like in this image. So I can control from admin side the list limit for every language.
Currently I use this pattern to create a custom input, but this is not language dependent:
File: admin/view/template/extension/theme/theme_default.tpl
<fieldset>
<div class="form-group required">
<label class="col-sm-2 control-label" for="inputId"><span data-toggle="tooltip" title="<?php echo $help_inputName; ?>"><?php echo $label_inputName; ?></span></label>
<div class="col-sm-10">
<input type="text" name="theme_default_inputName" value="<?php echo $theme_default_inputName; ?>" placeholder="<?php echo $label_inputName; ?>" id="inputId" class="form-control" />
<?php if ($error_inputName) { ?>
<div class="text-danger"><?php echo $error_inputName; ?></div>
<?php } ?>
</div>
</div>
</fieldset>
File: admin/language/en-gb/extension/theme/theme_default.php
//Language strings
$_['help_inputName'] = 'helpTxt';
$_['label_inputName'] = 'labelForInput';
$_['error_inputName'] = 'errorForInput';
File: admin/controller/extension/theme/theme_default.php
//Language strings
$text_strings = array(
'help_inputName',
'label_inputName',
'error_inputName'
);
foreach ($text_strings as $text) {
$data[$text] = $this->language->get($text);
}
//Error handling
if (isset($this->error['inputName'])) {
$data['error_inputName'] = $this->error['inputName'];
} else {
$data['error_inputName'] = '';
}
//Custom field
if (isset($this->request->post['theme_default_inputName'])) {
$data['theme_default_inputName'] = $this->request->post['theme_default_inputName'];
} elseif (isset($setting_info['theme_default_inputName'])) {
$data['theme_default_inputName'] = $setting_info['theme_default_inputName'];
} else {
$data['theme_default_inputName'] = "customText";
}
//Validation
if (!$this->request->post['theme_default_inputName']) {
$this->error['inputName'] = $this->language->get('error_inputName');
}