Internationalization: add translations.

frontend/src/locale/en.json

@@ -99,6 +99,10 @@
         "agent": "User agent",
         "searchQueries": "Search queries",
         "numberOfPosts": "Number of posts"
+      },
+      "drag": {
+        "title": "Upload a source file",
+        "description": "Drop your file here to add it as a source"
       }
     },
     "createAPIKey": {

frontend/src/locale/es.json

@@ -99,6 +99,10 @@
         "agent": "Agente de Usuario",
         "searchQueries": "Consultas de Búsqueda",
         "numberOfPosts": "Número de publicaciones"
+      },
+      "drag": {
+        "title": "Cargar un archivo fuente",
+        "description": "Suelta tu archivo aquí para agregarlo como fuente."
       }
     },
     "createAPIKey": {

frontend/src/locale/jp.json

@@ -99,6 +99,10 @@
         "agent": "ユーザーエージェント",
         "searchQueries": "検索クエリ",
         "numberOfPosts": "投稿数"
+      },
+      "drag": {
+        "title": "ソースファイルをアップロードする",
+        "description": "ファイルをここにドロップしてソースとして追加します"
       }
     },
     "createAPIKey": {

frontend/src/locale/zh-TW.json

@@ -92,6 +92,10 @@
         "agent": "使用者代理(User-Agent)",
         "searchQueries": "搜尋查詢",
         "numberOfPosts": "貼文數量"
+      },
+      "drag": {
+        "title": "上傳原始檔",
+        "description": "將您的文件拖放到此處以將其添加為來源"
       }
     },
     "createAPIKey": {

frontend/src/locale/zh.json

@@ -99,6 +99,10 @@
         "agent": "用户代理",
         "searchQueries": "搜索查询",
         "numberOfPosts": "帖子数量"
+      },
+      "drag": {
+        "title": "上传源文件",
+        "description": "将您的文件拖放到此处以将其添加为源"
       }
     },
     "createAPIKey": {