FontSwitcher.cs

#if UNITY_EDITOR
using System.Reflection;
using UnityEngine;
using UnityEditor;

public class FontSwitcher : EditorWindow
{
	[MenuItem("Font/Show Window")]
	public static void ShowFontWindow()
	{
		GetWindow<FontSwitcher>();
	}

	public void OnGUI ()
	{
		EditorGUI.BeginChangeCheck();
		string newFontName = EditorGUILayout.DelayedTextField("Unity Font", GUI.skin.font.fontNames[0]);
		if (EditorGUI.EndChangeCheck())
		{
			ReplaceFont((Font)EditorGUIUtility.LoadRequired("Fonts/Lucida Grande.ttf"), newFontName);
			ReplaceFont((Font)EditorGUIUtility.LoadRequired("Fonts/Lucida Grande Bold.ttf"), newFontName);
			ReplaceFont((Font)EditorGUIUtility.LoadRequired("Fonts/Lucida Grande Small.ttf"), newFontName);
			ReplaceFont((Font)EditorGUIUtility.LoadRequired("Fonts/Lucida Grande Small Bold.ttf"), newFontName);
			ReplaceFont((Font)EditorGUIUtility.LoadRequired("Fonts/Lucida Grande Big.ttf"), newFontName);

			typeof(EditorApplication).GetMethod("RequestRepaintAllViews", BindingFlags.Static | BindingFlags.NonPublic).Invoke(null, null);
		}
	}

	private void ReplaceFont(Font font, string fontName)
	{
		if (font.name.Contains("Bold"))
			font.fontNames = new string[] { fontName + " Bold" };
		else
			font.fontNames = new string[] { fontName };
		font.hideFlags = HideFlags.HideAndDontSave;
	}
}
#endif

I added some (two) things which refresh UI + Editor and font seems to be correctly updating in 2019.4.5, yay
I'd open a PR but not sure if gists can be treated like that lol probably not

https://gist.github.com/r618/0fe5e0f81a426cd05859dea778735471