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+# MSC4270: Matrix Glossary
+
+As the Matrix specification continues to grow, it becomes increasingly important to maintain consistent
+terms and phrases across clients, servers, and other implementations. Without this consistency, users
+may become confused when switching between implementations or potentially be unable to use another
+implementation entirely if the terminology is different enough.
+
+The specification already has some terminology contained in the [Appendices](https://spec.matrix.org/v1.13/appendices/),
+though the formal recommendation that users are called "users" is missing, for example. This proposal
+defines these historical terms in a new specification document on spec.matrix.org, called the Glossary.
+
+The new Glossary document may be further expanded through MSCs to include words or phrases which are
+critically needed for cross-implementation consistency. Translations to other languages are maintained
+through the MSC process, and published with the specification.
+
+## Proposal
+
+A new specification document titled "Glossary" is established, residing next to or near the existing
+[Appendices](https://spec.matrix.org/v1.13/appendices/) document. This new document has the following
+purpose/scope:
+
+* To define words, phrases, and terminology that implementations SHOULD use to provide consistent
+  user experience, especially when users are switching between implementations.
+* To affect clients, servers, and any other implementations of the Matrix Protocol.
+* To be accessible to the widest possible set of languages.
+
+The structure of the document is left as an editorial concern after this MSC is accepted. This MSC
+suggests sections covering broad categories with definitions contained within, as later represented
+by this proposal.
+
+Removing definitions from the specification requires an MSC, per normal [spec process](https://spec.matrix.org/proposals/).
+
+Adding or updating definitions MUST at minimum affect English definitions, and SHOULD include
+translations to the specification's accepted language list (defined later in this proposal). Both
+operations require an MSC, again per normal process, though the non-English translations MAY be
+affected by one or more follow-on MSCs after the English definitions are added. This is to say that
+an MSC which introduces new definitions might first land the English terms, and a future, second,
+MSC adds the French definitions for those English words, for example.
+
+The Spec Core Team (SCT) SHOULD consider how well definitions may translate to other languages before
+accepting English definitions into the spec, or seek professional external opinion on whether intent
+can be maintained through translations.
+
+### Initial definitions
+
+These definitions may be incorporated in a "General" section of the new Glossary document, and are
+normative (acceptance of this MSC means accepting the definitions).
+
+**TODO**: Re-add definitions once the remainder of the MSC has been reviewed. 😇
+
+### Initial language support
+
+The SCT does not have expertise in every language, and may be unable to reliably audit translations
+for a given language. To support the maximum possible set, within the bounds of professional translation
+services, the initial set of supported languages is as follows. A future MSC may add/remove/change this
+list. Contributions outside the supported languages list MAY be accepted on a case-by-case basis.
+
+* UK English
+* US English (where different from UK English)
+* French
+* German
+
+## Potential issues
+
+Some terms may not be easily translated or represented by non-English languages. The SCT is encouraged
+to request initial translations (where possible) on MSCs which introduce new English terms to the
+glossary.
+
+It's also possible that translations could change rapidly if there's disagreement about a given term's
+translation. The SCT is encouraged to review the source of translations for authenticity and trust
+before accepting an MSC.
+
+## Alternatives
+
+No notable alternatives.
+
+## Security considerations
+
+Translations may be from untrusted sources and could falsely represent the terms they claim to be
+translations for. As noted in the Potential Issues section, the SCT is encouraged to review the source
+of translations to avoid "trojan horse" contributions.
+
+## Unstable prefix
+
+Not applicable - this MSC covers text, not implementation.
+
+## Dependencies
+
+This MSC has no direct dependencies, but may be depended upon by other MSCs.
+
+[MSC4161](https://github.com/matrix-org/matrix-spec-proposals/pull/4161) is expected to make use of
+this MSC.