Hello all, I'll start this off with the usual...
If you break your $!#7, it ain't my fault! No one twisted your arm here. 
Anyway, I've noticed a few instances in these forums where someone will have questions about changing fonts so, I thought I would reprise my old
Sense 3.0/3.5 Thunderbolt tutorial from xda for those who would like to know the ins and outs of it. Of course, it's not necessary to go the manual route but, I think it's beneficial to anyone in the sense that it can give you a slightly more intimate understanding of how things work behind the scenes, AND it will allow you to show more consistency, when changing your fonts, than you would while using an app such as Rom Toolbox or the more specialized font changing apps.
A quick warning here, before you get started:
You SHALL find yourself in a bootloop if you fail to follow instructions!!
But, this is absolutely nothing to worry about, as long as you're prepared. Create a backup in SafeStrap prior to moving forward, if you haven't already. Should you find yourself in the bootloop, of which you were warned, there are merely two things you need to do:
1. (And this is HUGELY important) Shut the hell up! I hear you blaming me! I promise, YOU screwed up! lol
2. All you need to do is to perform an advanced restore from SafeStrap. Simply restore the System partition and don't worry about anything else. This should take less time than a full restore, which is unnecessary here.
So, here we go...
You'll need a root-enabled file explorer to do this. Root Explorer is my old stand-by but, Rom Toolbox also has one included. Another excellent option (coincidentally, a FREE option) is ES File Explorer. Any of these will work fine here.
To begin, I'll give you an idea of what you'll see in the "System/fonts" folder, as well as, offer an explanation for the purpose of the ones I know.
- AndroidClock.ttf = Stock Digital Clock Widget & Dock/Desk Clock ("Clock" in App Drawer).
- AndroidClock_Highlight.ttf = Lock Screen Clock.
- AndroidClock_Solid.ttf = Unsure of its purpose.
- Clockopia.ttf = Former Stock clock font but, seems unused by the system in Android 4.0+.
- DroidSans.ttf = Apparently unused in Android 4.0+. System font from previous Android versions.
- DroidSans-Bold = Apparently unused in Android 4.0+. Bold system font from previous Android versions.
- Roboto-Regular.ttf = This is the one always referred to as the "System Font." It yields the most noticeable results and, is the one all the font changer apps alter. Affects almost all text on your device.
- Roboto-Bold = The bold version of Roboto. Not seen everywhere but it is seen. Opening your Gmail app to an email in your inbox will allow you to see Regular and Bold in the same occurrence. The sender's name will be in bold and their address will be in Regular. I recommend changing if you have a bold version of your replacement font.
- Roboto-Italic = Unsure of its frequency of use but, it's not often. However, if you have a matching Italic font, it can't hurt to use it.
- Roboto-BoldItalic = Unsure of its frequency of use but, it's not often. However, if you have a matching Bold Italic font, it can't hurt to use it.
- There are also various other languages of the Roboto font in the "System/fonts" folder. If a particular language is your default, I'm sure it's obvious what adjustments you would need to make with regards to font replacement.
If however, you want more, this may be your thing. Here's what you do next. And it doesn't have to be done this way precisely but, I've found it to be much simpler than the alternatives.
1. You'll want to open your file explorer and navigate to the root of your SD-Ext card. Here you'll create a folder. Name it something you'll remember. It will contain copies of your personal fonts that you'll be wanting to use - just the ones which correspond to the System fonts you wish to be changed. Make the copies of your fonts and place them in this folder.
2. Re-name your fonts to PRECISELY match the names of their System font counterparts. P-R-E-C-I-S-E-L-Y!
IMPORTANT NOTE: Android DOES NOT recognize fonts with the "otf" or "open type font" file extension. It ONLY recognizes fonts with the "ttf" or "Truetype Font" file extension. In my experience though, you may simply change "otf" to "ttf" while re-naming them and they'll work fine.
Just so we're clear, here's an example.
If you're replacing Roboto-Bold.ttf,
with a font named Neutraface-Bold.otf,
you don't JUST change it to "Roboto-Bold.otf". You change it to "Roboto-Bold.ttf"
3. Now that you have all your fonts re-named to match their System Font counterparts, it's time to multi-select them all and either copy or move/cut (COPY is safer).
4. Navigate to the System folder, which is ABOVE the root of your SD card in the hierarchy. Within this folder, you'll find the "fonts" folder. Make sure your file explorer is set to "R/W" or "Read/Write" rather than the "RO" or "Read Only" setting. Once you've done this, paste your fonts within the "fonts" folder. When it asks you, select the box that says something to the effect of "do this for all" then allow it to overwrite the existing files.
5. We're almost there now! Next thing to do is to change permissions (Usually a long-press option) for each of the pasted font files. Right now their permissions read something like this - "rwxr-x".
It needs to read like this - "rw-r-r".
Bringing up the permissions options will probably look like nine check boxes arranged neatly in a square or rectangular pattern. That's three rows of three boxes.
x= a check
o= unchecked
o o o
x x x
x o x
OWNER= No Permissions
GROUP= Read and Write and Execute
OTHERS= Read and Execute
It needs to look like this when you're done. And it needs to be done for EVERY file you pasted in this folder.
x x o
x o o
x o o
OWNER= Read and Write
GROUP= Read
OTHERS= Read
6. Reboot and enjoy your triumph over The Man!
