Use English for verification error messages

Because the log page is more consistent in English.

xExtension-ReadingTime/extension.php

@@ -78,7 +78,7 @@ final class ReadingTimeExtension extends Minz_Extension {
 	/** @throws Minz_ConfigurationParamException */
 	private function validateSpeed(int $speed): int {
 		if ($speed <= 0) {
-			throw new Minz_ConfigurationParamException(_t('ext.reading_time.speed.invalid'));
+			throw new Minz_ConfigurationParamException('Reading speed must be greater than 0');
 		}
 		return $speed;
 	}
@@ -90,7 +90,7 @@ final class ReadingTimeExtension extends Minz_Extension {
 			case 'letters':
 				return $metrics;
 			default:
-				throw new Minz_ConfigurationParamException(_t('ext.reading_time.metrics.invalid'));
+				throw new Minz_ConfigurationParamException('Unsupported source metrics');
 		}
 	}
 }

xExtension-ReadingTime/i18n/en/ext.php

@@ -5,14 +5,12 @@ return array(
 		'speed' => array(
 			'label' => 'Reading speed',
 			'help' => 'Conversion factor to reading time from metrics',
-			'invalid' => 'Reading speed must be greater than 0',
 		),
 		'metrics' => array(
 			'label' => 'Source metrics',
 			'help' => 'Source of reading time calculation',
 			'words' => 'Number of words',
 			'letters' => 'Number of letters',
-			'invalid' => 'Unsupported source metrics',
 		),
 	),
 );

xExtension-ReadingTime/i18n/fr/ext.php

@@ -5,14 +5,12 @@ return array(
 		'speed' => array(
 			'label' => 'Vitesse de lecture',
 			'help' => 'Paramètre de calcul, dépendant de la méthode',
-			'invalid' => 'La vitesse de lecture doit être supérieure à 0',
 		),
 		'metrics' => array(
 			'label' => 'Méthodes',
 			'help' => 'Méthode de calcul du temps de lecture',
 			'words' => 'Nombre de mots',
 			'letters' => 'Nombre de lettres',
-			'invalid' => 'Méthode non prise en charge',
 		),
 	),
 );

xExtension-ReadingTime/i18n/ja/ext.php

@@ -5,14 +5,12 @@ return array(
 		'speed' => array(
 			'label' => '読書速度',
 			'help' => '基準値を読書時間に変換する係数',
-			'invalid' => '読書速度は0より大きい値でなければなりません',
 		),
 		'metrics' => array(
 			'label' => '基準値',
 			'help' => '読書時間を推定する基準値',
 			'words' => '単語数',
 			'letters' => '文字数',
-			'invalid' => 'サポートされていない基準値です',
 		),
 	),
 );