[IMP] base: do not allow to desactivate en_US
[IMP] base: do not allow to desactivate en_US

That would break a lot of methods (e.g. using formatLang method).
Closes #8659

hip-odoo/odoo,optima-ict/odoo,optima-ict/odoo,bplancher/odoo,stephen144/odoo,bplancher/odoo,syci/OCB,dfang/odoo,storm-computers/odoo,sysadminmatmoz/OCB,sysadminmatmoz/OCB,dfang/odoo,stephen144/odoo,dfang/odoo,ygol/odoo,hip-odoo/odoo,ygol/odoo,laslabs/odoo,stephen144/odoo,storm-computers/odoo,hip-odoo/odoo,stephen144/odoo,dfang/odoo,laslabs/odoo,hip-odoo/odoo,syci/OCB,syci/OCB,optima-ict/odoo,ygol/odoo,sysadminmatmoz/OCB,ygol/odoo,sysadminmatmoz/OCB,bplancher/odoo,microcom/odoo,Elico-Corp/odoo_OCB,bplancher/odoo,dfang/odoo,storm-computers/odoo,storm-computers/odoo,optima-ict/odoo,dfang/odoo,hip-odoo/odoo,bplancher/odoo,microcom/odoo,syci/OCB,ygol/odoo,stephen144/odoo,microcom/odoo,syci/OCB,hip-odoo/odoo,stephen144/odoo,optima-ict/odoo,laslabs/odoo,ygol/odoo,Elico-Corp/odoo_OCB,Elico-Corp/odoo_OCB,microcom/odoo,Elico-Corp/odoo_OCB,ygol/odoo,laslabs/odoo,sysadminmatmoz/OCB,sysadminmatmoz/OCB,laslabs/odoo,syci/OCB,Elico-Corp/odoo_OCB,storm-computers/odoo,Elico-Corp/odoo_OCB,laslabs/odoo,optima-ict/odoo,sysadminmatmoz/OCB,microcom/odoo,bplancher/odoo,microcom/odoo,storm-computers/odoo