To manually change your keyboard layout, type setxkbmap followed by the layout of your choice (gb for a uk keyboard map, fr for a french one, etc):

   setxkbmap gb

   
 us              USA
 ad              Andorra
 af              Afghanistan
 ara             Arabic
 al              Albania
 am              Armenia
 az              Azerbaijan
 by              Belarus
 be              Belgium
 bd              Bangladesh
 in              India
 ba              Bosnia and Herzegovina
 br              Brazil
 bg              Bulgaria
 ma              Morocco
 mm              Myanmar
 ca              Canada
 cd              Congo, Democratic Republic of the
 cn              China
 hr              Croatia
 cz              Czechia
 dk              Denmark
 nl              Netherlands
 bt              Bhutan
 ee              Estonia
 ir              Iran
 iq              Iraq
 fo              Faroe Islands
 fi              Finland
 fr              France
 gh              Ghana
 gn              Guinea
 ge              Georgia
 de              Germany
 gr              Greece
 hu              Hungary
 is              Iceland
 il              Israel
 it              Italy
 jp              Japan
 kg              Kyrgyzstan
 kh              Cambodia
 kz              Kazakhstan
 la              Laos
 latam           Latin American
 lt              Lithuania
 lv              Latvia
 mao             Maori
 me              Montenegro mk              Macedonia
 mt              Malta
 mn              Mongolia
 no              Norway
 pl              Poland
 pt              Portugal
 ro              Romania
 ru              Russia
 rs              Serbia
 si              Slovenia
 sk              Slovakia
 es              Spain
 se              Sweden
 ch              Switzerland
 sy              Syria
 tj              Tajikistan
 lk              Sri Lanka
 th              Thailand
 tr              Turkey
 ua              Ukraine
 gb              United Kingdom
 uz              Uzbekistan
 vn              Vietnam
 kr              Korea, Republic of
 nec_vndr/jp     Japan (PC-98xx Series)
 ie              Ireland
 pk              Pakistan
 mv              Maldives
 za              South Africa
 epo             Esperanto
 np              Nepal
 ng              Nigeria
 et              Ethiopia
 braille         Braille
   

For a complete overview, see: /usr/share/X11/xkb/rules/xorg.lst. To view the list:

  nano /usr/share/X11/xkb/rules/xorg.lst

In order to be able to type AltGr char, such as |, {, ~ etc .. type the following:

   setxkbmap -option lv3:rwin_switch,apple:badmap

Then use the right apple key as AltGr key to access these characters.