I am looking for a step by step method for enabling write in indian languages (hindi and gujarati) in Ubuntu applications (browser, LibreOffice, Pidgin etc..).
Could anyone please provide me a method for beginner to do it or simply direct me to the one if you know?
I updated this answer to Ubuntu 24.04 and above and removed the instructions for the older versions. The menus and settings have changed changed significantly since Ubuntu 18.04.
Go to System Menu at the top right corner of the desktop panel and select Settings, the gear/cog icon.
Select systems on the left panel first. Select Region & Languages from the right panel.
Click on Manage installed languages under System. A new window will open
click on the Install/Remove Languages... button. Another window will open. Scroll down and check the boxes for Hindi and Gujarati (and any other Indian languages you want). Then click the Apply button below. 
You will have to enter your sudo password in the Authentication Required window. This will install the ibus-m17n language library.
Close all applications and restart the computer for the ibus-m17n based keyboard layouts to show up in the list.
Select Keyboard on the left panel first. Select + Add Input Source from the right panel. 
Click on the three dots at the bottom to show more languages. 
Type Hindi or any other language you want to install. The word Other will show on the top of the Window.
Click on Other different keyboard layouts for Hindi (or the language you typed) will show below it.
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!
Repeat the steps above.
Here are the choices for Gujarati keyboard layouts: 
Other languages like Bengali has more choices:
To check the keyboard layouts of the languages you selected click on the three dots next to the language and then select View Keyboad Layout
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.
ibus-m17nThe language library ibus-m17n should be installed already. However, 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.
Open a terminal by pressing Ctrl+Alt+T and enter:
sudo apt install ibus-m17n
Enter your password when prompted.
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.
Avro is a popular English to Bengali phonetic keyboard layout. While ibus-m17n include quite a few Bangla keyboard layouts, Avro is not in included in ibus-m17n. Install ibus-avro if you want the Avro Bangla keyboard layout:
sudo apt install ibus-avro
Reboot the computer to see the Avro keyboard layout in settings.
See Why can't I find the App Avro Phonetic even though the software center shows it as installed? for more details.
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.
Hope this helps.
In order to type Indian languages or any other languages in Linux 11.1 and above, one need to install fonts of those languages and keyboard input method amd ibus m17n
For Indian languages open terminal and run the following commands:
sudo apt-get install ttf-indic-fonts
sudo apt-get install ibuspressing both keys
sudo apt-get install ibus-m17n
Restart the computer. Then from the dash (press Super) select System Settings and then Language Support (close any other window jf appears).
Goto keyboard input method system and choose ibus from the list to enable ibus.
Then from dash, search and select Keyboard Input Methods and and right click on icon, if it is not installed select install.
After this select Keyboard Input Methods and select launch, Ibus preferences menu will appear.
In "General" tab, mark for show icon on the system tray.
Now select second tab "Input Method", mark Customize active input methods then select an input method from the list (click on list icon to select from the language list) like Gujarati (choose one of these- in-script, itran or phonetic) selected language will appear under Customize active input methods.
Then click add option on the right side. For Hindi select Hindi -> (choose one option from 6 options, select phonetic m17n to type as you speak; भारत = Shift + bart) and click add next to it. Close the ibus preference menu.
Like this one can select any language from the list and add to language panel.
In any editor to activate desired language click on the language panel (right top corner of the screen) and select language in which you want to type. When you select language, icon will change to that language. To type in English select option - input method off.
In older version of Linux, Ctrl + Space, activates and deactivates the desired language.
The Hindi language keyboard code is hi and the Gujarati is gu
To add the support
Just press Ctrl+Alt+T on your keyboard to open Terminal. When it opens, run the commands below.
setxkbmap -option grp:switch,grp:alt_shift_toggle,grp_led:scroll us,hi
Or
setxkbmap -option grp:switch,grp:alt_shift_toggle,grp_led:scroll us,gu
Keep in mind that the above will go away once you reboot.
Using GUI open System settings, go to keyboard layout, and add the layout that you desire.
Press
Ctrl + Alt + T
The terminal window opens
Type
sudo synaptic
The synaptic window opens
Go to the search tool and search for the package iok
In the window that appears tick the box left to iok
Click on mark for installation
Click on Apply
Again click on Apply
Click on Close
Now search for ibus
In the window that appears search for ibus and tick the box to the left of it
Click on mark for installation
Click on apply
Again click on apply
Click on close
Close Synaptic
Go to settings
System Settings window opens, go to Language Support icon and click on it
In the Language Support window that appears click on Install/Remove languages
Browse for Hindi and tick on the box right to it.
Click on apply
Close Language Support and System Settings Windows
Go to Dash
Type iok and click on the iok icon that appears
iok -Indic Onscreen Keyboard opens
In the Right Bottom select hindi-inscript
New keyboard layout appears
Open libreoffice or gedit or any other text editor application
Press the key combination
super + space
start typing in Hindi
नमस्ते, मेरा नाम रैन्चो है|
Again to switch back to English typing press the key combination
super + space
