Commas and dots are ambiguous in international communication

Spaces has been endorsed by international standards such as SI/ISO 31-0.

wiki/src/contribute/how/documentation/style_guide.mdwn

@@ -12,6 +12,17 @@
     - Tails 3.0 is based on Debian 9 (Stretch)
     - *Tails Installer* is available on Ubuntu 15.10 (Wily Werewolf) or later.
 
+- **digit grouping**
+
+  Use a thin space (HTML entity: ` `) or a space to separate
+  groups of three digits.
+
+  * *For example*:
+    - $50 000
+
+  See [[!wikipedia Decimal_separator#Digit_grouping]] and [[!wikipedia
+  ISO_31-0#Numbers]].
+
 - **graphics card**
 
   And not *graphics adapters*, *graphics*, *graphical hardware*, or

wiki/src/news/duckduckgo_challenge.mdwn

@@ -8,7 +8,7 @@ on your support.</em> <small>([Edward
 Snowden](https://twitter.com/Snowden/status/975827513321623553))</small>
 
 Through our winter 2017/2018 donation campaign we managed to raise
-~103,000€, which is nearly half of our yearly budget for core work and
+~103&thinsp;000€, which is nearly half of our yearly budget for core work and
 maintenance. A big thanks to everybody who donated!
 
 To fill the gap, we are extremely happy to be part of [DuckDuckGo's
@@ -17,7 +17,7 @@ challenge](https://spreadprivacy.com/duckduckgo-privacy-challenge-2018/).
 
 Your donation is likely to be multiplied as it will be matched by
 DuckDuckGo and if we manage to raise enough by the end of the challenge
-on April 10th 2018, we might even receive a bonus up to $50,000.
+on April 10th 2018, we might even receive a bonus up to $50&thinsp;000.
 
 [Donate to Tails via the DuckDuckGo donation challenge](https://www.crowdrise.com/tails-live)
 
@@ -28,7 +28,7 @@ traces you want to leave and those that you'd rather see forgotten.
 Installed onto a USB key, Tails discreetly fits into your pocket.
 
 For the past 9 years, we've been working on making digital security
-accessible to those who need it most. Counting more than 20,000 boots
+accessible to those who need it most. Counting more than 20&thinsp;000 boots
 per day, we've proved that Tails is a reliable and successful tool that
 helps diverse people around the world to be safe online every day. But
 we think that the immense work we've done until now should have an even