Spotifyの検索APIで検索をした際、コンソールとcurlでアーティスト名やトラック名が日本語で返ってこないことがあります。
例えば「水曜日のカンパネラ」で検索をしてみると、nameのところに「水曜日のカンパネラ」と日本語で文字が返ってきます。
https://developer.spotify.com/console/get-search-item/?q=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist&market=&limit=&offset=

{
  "artists": {
    "href": "https://api.spotify.com/v1/search?query=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist&market=JP&offset=0&limit=20",
    "items": [
      {
        "external_urls": {
          "spotify": "https://open.spotify.com/artist/0bp9CvkjQYhUJvWRHjFRWI"
        },
        "followers": {
          "href": null,
          "total": 74886
        },
        "genres": [
          "j-dance",
          "j-rock",
          "shibuya-kei"
        ],
        "href": "https://api.spotify.com/v1/artists/0bp9CvkjQYhUJvWRHjFRWI",
        "id": "0bp9CvkjQYhUJvWRHjFRWI",
        "images": [
          {
            "height": 640,
            "url": "https://i.scdn.co/image/7a4c7ce6ba3f6026110b37f6b6df697520c85dbf",
            "width": 640
          },
          {
            "height": 320,
            "url": "https://i.scdn.co/image/802457a9e1c49d765b5bbc11da67c8150c371758",
            "width": 320
          },
          {
            "height": 160,
            "url": "https://i.scdn.co/image/4c21f512b40e4614b74d1adb31ac9fc0e45d9a76",
            "width": 160
          }
        ],
        "name": "水曜日のカンパネラ",
        "popularity": 49,
        "type": "artist",
        "uri": "spotify:artist:0bp9CvkjQYhUJvWRHjFRWI"
      }
    ],
    "limit": 20,
    "next": null,
    "offset": 0,
    "previous": null,
    "total": 1
  }
}

これに対し、curlで叩いてみると、nameの箇所が"WEDNESDAY CAMPANELLA"と返ってきます。

curl -X "GET" "https://api.spotify.com/v1/search?q=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist" -H "Accept: application/json" -H "Content-Type: application/json" -H "Authorization: Bearer [Access Token]"

{
    "artists": {
        "href": "https://api.spotify.com/v1/search?query=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist&market=JP&offset=0&limit=20",
        "items": [
            {
                "external_urls": {
                    "spotify": "https://open.spotify.com/artist/0bp9CvkjQYhUJvWRHjFRWI"
                },
                "followers": {
                    "href": null,
                    "total": 74886
                },
                "genres": [
                    "j-dance",
                    "j-rock",
                    "shibuya-kei"
                ],
                "href": "https://api.spotify.com/v1/artists/0bp9CvkjQYhUJvWRHjFRWI",
                "id": "0bp9CvkjQYhUJvWRHjFRWI",
                "images": [
                    {
                        "height": 640,
                        "url": "https://i.scdn.co/image/7a4c7ce6ba3f6026110b37f6b6df697520c85dbf",
                        "width": 640
                    },
                    {
                        "height": 320,
                        "url": "https://i.scdn.co/image/802457a9e1c49d765b5bbc11da67c8150c371758",
                        "width": 320
                    },
                    {
                        "height": 160,
                        "url": "https://i.scdn.co/image/4c21f512b40e4614b74d1adb31ac9fc0e45d9a76",
                        "width": 160
                    }
                ],
                "name": "WEDNESDAY CAMPANELLA",
                "popularity": 49,
                "type": "artist",
                "uri": "spotify:artist:0bp9CvkjQYhUJvWRHjFRWI"
            }
        ],
        "limit": 20,
        "next": null,
        "offset": 0,
        "previous": null,
        "total": 1
    }
}

このnameを日本語で返したい場合、Accept-Languageヘッダーをリクエスト時に設定すれば良いようです。

先程のcurlに　 -H 'Accept-Language: ja;q=1'をつけて送信してみます。

curl -X "GET" "https://api.spotify.com/v1/search?q=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist" -H "Accept: application/json" -H "Content-Type: application/json" -H "Authorization: Bearer [Access Token]" -H 'Accept-Language: ja;q=1'

すると、webコンソールと同様の結果が返ってきます。

{
  "artists": {
    "href": "https://api.spotify.com/v1/search?query=%E6%B0%B4%E6%9B%9C%E6%97%A5%E3%81%AE%E3%82%AB%E3%83%B3%E3%83%91%E3%83%8D%E3%83%A9&type=artist&market=JP&offset=0&limit=20",
    "items": [
      {
        "external_urls": {
          "spotify": "https://open.spotify.com/artist/0bp9CvkjQYhUJvWRHjFRWI"
        },
        "followers": {
          "href": null,
          "total": 74886
        },
        "genres": [
          "j-dance",
          "j-rock",
          "shibuya-kei"
        ],
        "href": "https://api.spotify.com/v1/artists/0bp9CvkjQYhUJvWRHjFRWI",
        "id": "0bp9CvkjQYhUJvWRHjFRWI",
        "images": [
          {
            "height": 640,
            "url": "https://i.scdn.co/image/7a4c7ce6ba3f6026110b37f6b6df697520c85dbf",
            "width": 640
          },
          {
            "height": 320,
            "url": "https://i.scdn.co/image/802457a9e1c49d765b5bbc11da67c8150c371758",
            "width": 320
          },
          {
            "height": 160,
            "url": "https://i.scdn.co/image/4c21f512b40e4614b74d1adb31ac9fc0e45d9a76",
            "width": 160
          }
        ],
        "name": "水曜日のカンパネラ",
        "popularity": 49,
        "type": "artist",
        "uri": "spotify:artist:0bp9CvkjQYhUJvWRHjFRWI"
      }
    ],
    "limit": 20,
    "next": null,
    "offset": 0,
    "previous": null,
    "total": 1
  }
}

なぜwebコンソールで日本語表示ができているかというと、ブラウザの言語設定を日本語にしてAccept-Languageヘッダーが日本語で送信されたため、結果も日本語で表示されるようです。