In section 8. Default Language,

One Map contained in an @context Array MUST contain a name-value pair that defines the default language for the Thing Description, where the name is the Term @language and the value is a well-formed language tag as defined by [BCP47] (e.g., en, de-AT, gsw-CH, zh-Hans, zh-Hant-HK, sl-nedis).

1. This section has MUST clause to include default language in @context array, but examples in this spec (e.g. example 1, example 2, example 4) do not have such.
2. In 6.3.2 Human-Readable Metadata in WoT Things Description, handling of language is discussed in detail and fallback is also defined (like quoted below). This section seems not to be consisted with these.

When metadata such as @direction is not present, TD Consumers SHOULD use first-strong detection as a fallback. For the MultiLanguage Map, TD Consumers MAY infer the base direction from the language tag of the individual strings.

Also, there should be some mention about which language should be applied for reply of property request, write property, or action in protocol bindings.