zbik 's answer is awesome. But error will be raised if Selection field has False value.

Otherwise use this. 

<t t-set="values" t-value="dict([('A','Approved'),('D','Denied'), (False,False)])"/> 
<t t-esc="values[object.x_approval_status]"/>

Or

<t t-esc="{False: False, 'A': 'Approved', 'D': 'Denied'}[object.x_approval_status]"/>

if you want to get rid of False error

It should also work

<t t-if = "object. x_approval_status">
<t t-esc = "dict (object.fields_get (allfields = ['x_approval_status']) ['x_approval_status'] ['selection']) [object.x_approval_status]" />
</t>

Another solution:
use <t t-field="o.your_field"/>

Worked wonderfully well, big thanks for quick reply !!

Just wanted to chime in and say that zbik's answer also works in email templates. This is an example that can be used in contracts reminder:

${dict(object.fields_get(allfields=['recurring_rule_type'])['recurring_rule_type']['selection'])[object.recurring_rule_type]}

Thanks, Zbik, I used your suggestion in my case for each order line to html orders report as a list, and it's working in v.11:

<t t-esc="dict(doc.order_id.fields_get(allfields=['my_field_in_SO'])['my_field_in_SO']['selection'])[doc.order_id.my_field_in_SO]"/>