For Ubuntu 18.04 and above

The menus and settings have changed changed significantly since Ubuntu 17.10 and above uses Gnome Shell instead of Unity. These instructions may work for Ubuntu 17.10 as well, but I have only tested them in Ubuntu 18.04 LTS.

Use a Hindi keyboard:

1. Go to System Menu at the top right corner of the desktop panel and
   select Settings, the screwdriver & wrench icon.

   
   

   

   
   



2. Select Region & Languages

   
   



3. Click the + icon under the Input Sources to open Add an Input Source window.

   
   

   

   
   



4. Click on the three dots at the bottom of the window to expose the
   search bar.

   
   

   

   
   



5. Type Hindi or any other language you want to install.
   The word Other will show on the top of the Window.

   
   



6. Click on Other different keyboard layouts for Hindi (or the language you typed) will show below it.

   
   

   

   
   



7. Select a keyboard layout and press the Add button at the top.

   
   

   

   
   

   Now the new keyboard layout will be listed in the Input Sources table.

   
   

   

   
   

That's it!

For Gujarati and other Indian languages

Repeat the steps above.

There is only one keyboard layout available by default for Gujarati.

Check the keyboard layouts you selected first select the language from the list of input sources. Then click on the keyboard icon at the bottom right corner.

You can also see the keyboard layouts of any installed language from the drop-down menu of the language icon on the top right corner of the desktop.

Use ibus-m17n, the preferred method

If you don't see the keyboard layout you want, or if you get unexpected results when you type in the selected language then follow the steps below install ibus-m17n. This will give you more choices of keyboard layouts in your Indian language.

1. Open a terminal by pressing Ctrl+Alt+T and enter:

   
   

   sudo apt install ibus-m17n
   
   

   
   



2. Enter your password when prompted.

   
   



3. Close all applications and restart the computer for the
   ibus-m17n based keyboard layouts to show up in the list. Follow the
   same steps to select a different keyboard layout.

   
   

Changing between keyboard layouts

Once a new keyboard layout is selected, you will see a new language icon at the top panel. Clicking it will give you all the installed keyboard layout choices. You can also switch between different installed keyboard layouts by clicking Super+Space, or Shift+Super+Space.

Instructions for older versions of Ubuntu

For Ubuntu 16.04

Install language support

Go to System Settings > Language Support > Install Languages and install Hindi (or any other Indian language).

Use a Hindi keyboard:

1. Go to the Keyboard app. If you have Unity or something that allows you to search for your apps, then get to it that way. Otherwise it's probably in System » Preferences » Keyboard.


2. Go to Text Entry at the bottom of the Typing tab. Click add, and find Hindi (it's easier by language than by country).


3. Choose a keyboard layout you are comfortable with. The program will display the layout so you can confirm the one that suits you best. Examples of keyboard layouts are Bolnagiri, KaGaPa, Phonetic, and Wx. different layouts assign different keys to different letters. Choose the keyboard layout you are used to, or try a few and see which one you like best. Here are some examples of Hindi keyboard layouts.


4. A little icon on the top panel displays a small keyboard icon and the current keyboard layout. It's probably still the English language one, since you haven't yet chosen to write in Hindi. So, to start writing in Hindi, click on that icon and choose the Hindi layout. You can now start typing in Hindi.

Repeat for Gujarati. When you do it for the first time, it will ask permission to install some software. Say yes and enter password when needed.

Use ibus-m17n, the preferred method

1. Using Ubuntu Software Center install ibus-m17n. This will give
   you more Hindi keyboard layout choices. This may be already
   installed.


2. Once you installed iBus, open Dash and look for iBus. Once iBus is
   running, go to the second tab called input method.


3. Make sure "Customize Input Selection Method" is checked. Click on
   Select and Input Method and select Hindi > itrans. Then hit the
   Add button to add this input method. If Hindi is not at the top, click on it and click "Up" button to move it to the top. Click on close button. You will
   notice a keyboard icon on the top panel in Unity.

Some hints on typing in Hindi (Itrans)

Now, open a new window of LibreOffice or Gedit or where ever you want to type in Hindi and hit Super+Space Bar. This will change the input method to Hindi for that app. You will notice that the icon on the tray now shows Hindi क्. If you don't see क् and see the keyboard icon or another language icon on the top panel, click on it and select Hindi-Itrans (m17n). Now type "kaise ho" it should appear in Hindi.

Note the Itrans phonetic layout has its own rules so it may not be exactly what you are used to. There is a Gujarati-Itrans choice as well in the ibus Input selection method.

More detailed instructions with pictures.

See the answer to How to type half Hindi character with Hindi (Bolnagri) layout?

Hope this helps.