Cloud Functionsのmain.pyで下記ソースコードを実行してCloud Functionsに入っているフォント一覧を確認しました。

ソースコード

main.py

import functions_framework
import matplotlib.font_manager

@functions_framework.http
def hello_http(request):
  # 利用可能なフォントのリストを取得
  font_list = matplotlib.font_manager.findSystemFonts()

  # フォントリストを表示
  for font_path in font_list:
    print(font_path)
  
  return 'Hello {}!'.format(font_list)

requirements.txt

functions-framework==3.*
 matplotlib

フォント一覧

/usr/share/fonts/opentype/ipafont-mincho/ipamp.ttf
/usr/share/fonts/truetype/fonts-japanese-mincho.ttf
/usr/share/fonts/truetype/liberation/LiberationSans-Regular.ttf
/usr/share/fonts/truetype/kacst/KacstTitleL.ttf
/usr/share/fonts/truetype/freefont/FreeSerifItalic.ttf
/usr/share/fonts/truetype/tlwg/Garuda-Bold.ttf
/usr/share/fonts/truetype/tlwg/Umpush-LightOblique.ttf
/usr/share/fonts/truetype/tlwg/Waree-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Sawasdee-Oblique.ttf
/usr/share/fonts/truetype/kacst/KacstQurn.ttf
/usr/share/fonts/truetype/kacst/KacstScreen.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypewriter-BoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Kinnari-Bold.ttf
/usr/share/fonts/truetype/freefont/FreeSerifBold.ttf
/usr/share/fonts/opentype/ipafont-gothic/ipagp.ttf
/usr/share/fonts/truetype/tlwg/Kinnari.ttf
/usr/share/fonts/truetype/tlwg/TlwgMono.ttf
/usr/share/fonts/truetype/tlwg/Laksaman.ttf
/usr/share/fonts/truetype/tlwg/Loma-BoldOblique.ttf
/usr/share/fonts/opentype/ipafont-mincho/ipam.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypo-BoldOblique.ttf
/usr/share/fonts/truetype/liberation/LiberationSans-Bold.ttf
/usr/share/fonts/truetype/wqy/wqy-zenhei.ttc
/usr/share/fonts/truetype/freefont/FreeSansBoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Garuda-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Loma.ttf
/usr/share/fonts/truetype/tlwg/TlwgMono-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Umpush-BoldOblique.ttf
/usr/share/fonts/truetype/kacst/KacstBook.ttf
/usr/share/fonts/truetype/liberation/LiberationSansNarrow-Italic.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypist.ttf
/usr/share/fonts/truetype/tlwg/TlwgMono-BoldOblique.ttf
/usr/share/fonts/truetype/liberation/LiberationSansNarrow-BoldItalic.ttf
/usr/share/fonts/truetype/freefont/FreeSansOblique.ttf
/usr/share/fonts/truetype/tlwg/Norasi-BoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Sawasdee.ttf
/usr/share/fonts/truetype/tlwg/Sawasdee-BoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Purisa.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypist-Bold.ttf
/usr/share/fonts/truetype/kacst/KacstDigital.ttf
/usr/share/fonts/truetype/kacst/KacstPen.ttf
/usr/share/fonts/truetype/liberation/LiberationSerif-BoldItalic.ttf
/usr/share/fonts/truetype/liberation/LiberationMono-BoldItalic.ttf
/usr/share/fonts/truetype/tlwg/TlwgMono-Bold.ttf
/usr/share/fonts/truetype/kacst/KacstLetter.ttf
/usr/share/fonts/truetype/tlwg/Kinnari-Italic.ttf
/usr/share/fonts/truetype/tlwg/Waree-BoldOblique.ttf
/usr/share/fonts/truetype/freefont/FreeSansBold.ttf
/usr/share/fonts/truetype/liberation/LiberationSerif-Regular.ttf
/usr/share/fonts/truetype/fonts-japanese-gothic.ttf
/usr/share/fonts/truetype/tlwg/Norasi.ttf
/usr/share/fonts/truetype/freefont/FreeSans.ttf
/usr/share/fonts/truetype/tlwg/Purisa-Bold.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypo-Bold.ttf
/usr/share/fonts/truetype/tlwg/Kinnari-BoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Kinnari-BoldItalic.ttf
/usr/share/fonts/truetype/tlwg/Waree-Bold.ttf
/usr/share/fonts/truetype/liberation/LiberationSans-BoldItalic.ttf
/usr/share/fonts/truetype/freefont/FreeMonoBold.ttf
/usr/share/fonts/truetype/liberation/LiberationMono-Italic.ttf
/usr/share/fonts/truetype/liberation/LiberationSerif-Italic.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypist-BoldOblique.ttf
/usr/share/fonts/truetype/liberation/LiberationSerif-Bold.ttf
/usr/share/fonts/truetype/kacst/KacstArt.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypewriter-Bold.ttf
/usr/share/fonts/truetype/tlwg/Umpush-Oblique.ttf
/usr/share/fonts/truetype/liberation/LiberationMono-Bold.ttf
/usr/share/fonts/truetype/freefont/FreeMono.ttf
/usr/share/fonts/truetype/tlwg/Laksaman-Italic.ttf
/usr/share/fonts/truetype/kacst/KacstDecorative.ttf
/usr/share/fonts/truetype/freefont/FreeSerifBoldItalic.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypo-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Laksaman-BoldItalic.ttf
/usr/share/fonts/truetype/kacst/KacstTitle.ttf
/usr/share/fonts/truetype/tlwg/Laksaman-Bold.ttf
/usr/share/fonts/truetype/kacst/KacstFarsi.ttf
/usr/share/fonts/truetype/tlwg/Purisa-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Sawasdee-Bold.ttf
/usr/share/fonts/truetype/tlwg/Purisa-BoldOblique.ttf
/usr/share/fonts/truetype/liberation/LiberationMono-Regular.ttf
/usr/share/fonts/truetype/freefont/FreeMonoOblique.ttf
/usr/share/fonts/truetype/freefont/FreeMonoBoldOblique.ttf
/usr/share/fonts/truetype/tlwg/Loma-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Loma-Bold.ttf
/usr/share/fonts/truetype/kacst-one/KacstOne.ttf
/usr/share/fonts/truetype/tlwg/Kinnari-Oblique.ttf
/usr/share/fonts/truetype/liberation/LiberationSansNarrow-Bold.ttf
/usr/share/fonts/truetype/droid/DroidSansFallbackFull.ttf
/usr/share/fonts/truetype/liberation/LiberationSans-Italic.ttf
/usr/share/fonts/truetype/freefont/FreeSerif.ttf
/usr/share/fonts/truetype/liberation/LiberationSansNarrow-Regular.ttf
/usr/share/fonts/truetype/kacst/KacstOffice.ttf
/usr/share/fonts/truetype/kacst/mry_KacstQurn.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypewriter-Oblique.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypo.ttf
/usr/share/fonts/truetype/tlwg/Norasi-Bold.ttf
/usr/share/fonts/truetype/noto/NotoMono-Regular.ttf
/usr/share/fonts/truetype/kacst/KacstNaskh.ttf
/usr/share/fonts/truetype/tlwg/Norasi-Italic.ttf
/usr/share/fonts/truetype/tlwg/Waree.ttf
/usr/share/fonts/truetype/tlwg/Norasi-Oblique.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypewriter.ttf
/usr/share/fonts/opentype/ipafont-gothic/ipag.ttf
/usr/share/fonts/truetype/tlwg/TlwgTypist-Oblique.ttf
/usr/share/fonts/truetype/tlwg/Garuda.ttf

日本語に対応しているフォント

chatGPT-3.5に日本語に対応しているフォントがどれか聞いてみた。
以下回答

提供されたフォントリストの中から、日本語に対応しているフォントを見つけることができます。日本語に対応しているフォントは、一般的に日本語の文字セットを含んでいる必要があります。以下のフォントは日本語に対応しています：

/usr/share/fonts/truetype/fonts-japanese-mincho.ttf
日本語明朝体フォントです。日本語の漢字やひらがな、カタカナなどが含まれています。

/usr/share/fonts/truetype/wqy/wqy-zenhei.ttc
WenQuanYi Zen Hei（文泉驛黒体）とも呼ばれ、日本語のフォントにも対応しています。

/usr/share/fonts/opentype/ipafont-mincho/ipamp.ttf
IPAフォントの明朝体バージョンで、日本語に対応しています。

上記のフォントは日本語の文字をサポートしており、日本語のテキスト表示に適しています。他のフォントも含まれていますが、日本語対応フォントはこれらのフォントです。